Performance Results for 

Massachusetts and Rhode 

Island Deep Energy Retrofit 

Pilot Community

C. Gates and K. Neuhauser

Building Science Corporation

March 2014
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States 

government. Neither the United States government nor any agency thereof, nor any of their 

employees, subcontractors, or affiliated partners makes any warranty, express or implied, or assumes 

any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, 

apparatus, product, or process disclosed, or represents that its use would not infringe privately owned 

rights. Reference herein to any specific commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, 

recommendation, or favoring by the United States government or any agency thereof. The views and 

opinions of authors expressed herein do not necessarily state or reflect those of the United States 

government or any agency thereof.

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energy

and its contractors, in paper, from:

U.S. Department of Energy

Office of Scientific and Technical Information

P.O. Box 62

Oak Ridge, TN 37831-0062

phone: 865.576.8401

fax: 865.576.5728

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from:

U.S. Department of Commerce

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

phone: 800.553.6847

fax: 703.605.6900

email: orders@ntis.fedworld.gov

online ordering: http://www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
iii

Performance Results for Massachusetts and Rhode Island 

Deep Energy Retrofit Pilot Community

Prepared for:

The National Renewable Energy Laboratory

On behalf of the U.S. Department of Energy’s Building America Program

Office of Energy Efficiency and Renewable Energy

15013 Denver West Parkway

Golden, CO 80401

NREL Contract No. DE-AC36-08GO28308

Prepared by: 

C. Gates and K. Neuhauser

Building Science Corporation

30 Forest Street

Somerville, MA 02143

NREL Technical Monitor: Cheryn Metzger

Prepared under Subcontract No. KNDJ-0-40337-03

March 2014
iv

[This page left blank]
v

Contents

List of Figures ............................................................................................................................................ vi

List of Tables ............................................................................................................................................. vii

Definitions................................................................................................................................................. viii

Executive Summary................................................................................................................................... ix

1 Introduction........................................................................................................................................... 1

2 Background........................................................................................................................................... 3

2.1 New Construction, Retrofits, and DERs..............................................................................3

2.2 Previous Work .....................................................................................................................4

2.3 Building Science Corporation and the National Grid DER Pilot Program..........................5

3 National Grid Deep Energy Retrofit Pilot Program ........................................................................... 6

3.1 Measures and Targets ..........................................................................................................6

3.2 The Community of Retrofits................................................................................................8

4 Energy Use Results and Analysis..................................................................................................... 18

4.1 Reduction Versus Performance Achieved .........................................................................18

4.2 Site and Source Energy......................................................................................................19

4.3 On-Site Generation ............................................................................................................19

4.4 Energy Use Data ................................................................................................................19

4.4.1 Energy Use Data Normalization and Disaggregation............................................25

4.5 Characterization of Post-Retrofit Energy Use ...................................................................29

4.5.1 Pre- and Post-Retrofit Energy Use Comparison ....................................................29

4.5.2 Post-Retrofit Energy Use per Household...............................................................36

4.5.3 Post-Retrofit Energy Use Intensity ........................................................................41

4.6 Impact of Retrofit Package Variations...............................................................................46

4.6.1 Heating Fuel Source...............................................................................................46

4.6.2 Included Versus Excluded Basement.....................................................................47

4.6.3 Unvented Versus Vented Attic ..............................................................................50

4.6.4 Airtightness Versus Post-Retrofit Energy Use ......................................................52

4.7 Conclusions of Energy Use Analysis.................................................................................53

5 Airtightness Results and Analysis ................................................................................................... 55

5.1 Airtightness Test Results ...................................................................................................58

5.2 Analysis of Airtightness and DER Package Variations.....................................................62

5.2.1 Inclusion/Exclusion of Basement in Air Control Enclosure..................................62

5.2.2 Vented/Unvented Attic ..........................................................................................64

5.2.3 Air Control Materials.............................................................................................66

5.3 Airtightness Trends Observed in the DER Community ....................................................72

6 Construction Cost Analysis .............................................................................................................. 73

6.1 Summary of Energy-Related Construction Costs..............................................................73

6.2 Energy-Related Construction Costs per DER Measure .....................................................83

6.2.1 Attic/Roof DER Measure.......................................................................................83

6.2.2 Exterior Wall DER Measure..................................................................................83

7 Homeowner Satisfaction.................................................................................................................... 86

8 Conclusions ........................................................................................................................................ 87

References................................................................................................................................................. 91

Appendix: Homeowner Survey................................................................................................................ 94
vi

List of Figures

Figure 1. U.S. housing units by decade of construction ........................................................................ 3

Figure 2. Pre- and post-retrofit site energy use for all DER projects .................................................. 30

Figure 3. Pre- and post-retrofit source energy use for all DER projects............................................. 31

Figure 4. Energy use reduction (percent reduction) achieved in terms of both site and source 

energy for all DER projects ............................................................................................................... 32

Figure 5. Site energy use percent reduction relative to pre-retrofit site energy use......................... 33

Figure 6. Source energy use percent reduction relative to pre-retrofit source energy use.............. 33

Figure 7. Site energy use percent reduction relative to pre-retrofit conditioned floor area ............. 34

Figure 8. Source energy use percent reduction relative to pre-retrofit conditioned floor area........ 34

Figure 9. Site energy use percent reduction relative to pre-retrofit air leakage measurement........ 35

Figure 10. Source energy use percent reduction relative to pre-retrofit air leakage measurement 35

Figure 11. Site energy use percent reduction relative to approximate year of construction ........... 36

Figure 12. Source energy use percent reduction relative to approximate year of construction...... 36

Figure 13. Post-retrofit site MMBtu/year per household....................................................................... 39

Figure 14. Post-retrofit source MMBtu/year per household ................................................................. 40

Figure 15. Post-retrofit site EUI (kBtu/ft2∙yr)........................................................................................... 42

Figure 16. Post-retrofit source EUI (kBtu/ft2∙yr)..................................................................................... 43

Figure 17. Source EUI relative to post-retrofit conditioned floor area for comprehensive DERs .... 44

Figure 18. Post-retrofit source EUI and post-retrofit conditioned floor area...................................... 45

Figure 19. Post-retrofit source EUI grouped by heat and DHW fuel source with post-retrofit 

conditioned floor area........................................................................................................................ 48

Figure 20. Post-retrofit heating and cooling source EUI by basement treatment.............................. 49

Figure 21. Post-retrofit heating and cooling source EUI grouped by attic and roof treatment ........ 51

Figure 22. Post-retrofit heating and cooling EUIs relative to post-retrofit ACH50............................. 52

Figure 23. Post-retrofit heating and cooling energy use per household relative to post-retrofit 

ACH50 .................................................................................................................................................. 52

Figure 24. Pre-DER and post-DER total CFM50 results ........................................................................ 59

Figure 25. Percent reduction from pre-DER to post-DER total CFM50 ............................................... 60

Figure 26. Post-DER ACH50 results........................................................................................................ 61

Figure 27. Post-DER ACH50 versus size of house, year house was built, and pre-DER total CFM5061

Figure 28. Post-DER ACH50 results grouped by treatment of basement ........................................... 63

Figure 29. Post-DER ACH50 results grouped by treatment of attic/roof treatment ........................... 65

Figure 30. Post-DER ACH50 results grouped roof and wall air control material ............................... 68

Figure 31. Post-DER ACH50 results grouped use of SPF insulation in walls and roof..................... 69

Figure 32. Post-DER ACH50 results grouped by non-adhered/fully adhered roof underlayment.... 71

Figure 33. Total project and total energy-related costs normalized by conditioned floor area for full 

DER projects ....................................................................................................................................... 78

Figure 34. Total project and total energy-related costs normalized by enclosure area for full DER 

project.................................................................................................................................................. 79

Figure 35. Total energy-related enclosure costs normalized by treated enclosure area for all DER 

projects................................................................................................................................................ 81

Figure 36. Total energy-related HVAC costs normalized by living units in building and grouped by 

function................................................................................................................................................ 82

Figure 37. Total energy-related attic roof costs per attic/roof square foot......................................... 84

Figure 38. Total energy-related exterior wall costs per wall square foot............................................ 85

Unless otherwise noted, all figures were created by BSC.
vii

List of Tables

Table 1. Overall Measures and Targets or Requirements for National Grid DER Pilot Retrofit.......... 7

Table 2. Enclosure Insulation Measures and Targets for National Grid DER Pilot Retrofit................ 7

Table 3. HVAC Measures and Targets for National Grid DER Pilot Retrofit ......................................... 8

Table 4. DER Community—37 Comprehensive DERs............................................................................. 9

Table 5. DER Community—5 Partial DERs............................................................................................. 15

Table 6. Source-Site Ratios for All Portfolio Manager Fuels ................................................................ 19

Table 7. DER Community Pre-Retrofit Energy Use—12 Months.......................................................... 21

Table 8. DER Community Post-Retrofit Energy Use ............................................................................. 23

Table 9. Summary of DER Community Pre- and Post-Retrofit Energy Use, Normalized Post-Retrofit 

Energy Use, and Normalized Heating and Cooling Post-Retrofit Energy Use............................ 27

Table 10. Heating Fuel and Source EUI .................................................................................................. 46

Table 11. Air Barrier Material/Air Control Layer Key for Data Tables Below ...................................... 55

Table 12. DER Community Test Results and Air Control System Properties–Full DERs ................. 56

Table 13. DER Community Test Results and Air Control System Properties–Partial DERs............. 57

Table 14. Summary of National Grid DER Project Costs as Derived From Program Application 

Forms—Full DERs .............................................................................................................................. 74

Table 15. Summary of National Grid DER Project Costs as Derived from Program Application 

Forms—Partial DERs ......................................................................................................................... 76

Unless otherwise noted, all tables were created by BSC.
viii

Definitions

ACH Air changes per hour 

ACH50 Air changes per hour at 50 Pascal test pressure

AFUE Annual fuel utilization efficiency

ASHP Air source heat pump

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning 

Engineers

BA Building America Program

BSC Building Science Corporation

Btu British thermal unit

CDD Cooling degree day

CFM50 Cubic feet per minute at 50 Pascal test pressure

DER Deep energy retrofit

DHW Domestic hot water or service hot water

EIA Energy Information Administration

EPA U.S. Environmental Protection Agency

ERV Energy recovery ventilator

EUI Energy use intensity

ft2 Square foot, square feet

GSHP Ground source heat pump

HDD Heating degree day

HRV Heat recovery ventilator

kBtu Thousand British thermal units

kWh Kilowatt-hour

MMBtu Million British thermal units

OSB Oriented strand board

RECS Residential Energy Consumption Survey

SPF Spray polyurethane foam (insulation)

TMY3 Typical Meteorological Year 3
ix

Executive Summary

Between December of 2009 and December of 2012, participants in a deep energy retrofit (DER) 

pilot program sponsored by National Grid and conducted in Massachusetts and Rhode Island 

completed 42 DER projects. Building Science Corporation (BSC) provided technical support to 

program participants and verification of measures for the program sponsor, National Grid. The 

pilot program required aggressive upgrades to building enclosure systems, implementation of 

ventilation and combustion safety measures, and also provided incentives to upgrade mechanical 

systems. Thirty-seven of the projects completed through the pilot were comprehensive retrofits 

while five were partial DERs, meaning that high performance retrofit was implemented for a 

single major enclosure component or a limited number of major enclosure components. The 

collection of 42 DER projects represents 60 units of housing. 

Pre- and post-retrofit air leakage measurements were performed for each of the projects. Each 

project also reported information about project costs including identification of energy-related 

costs. Pilot program application forms collected pre-retrofit energy use data for 35 of the projects. 

BSC used energy modeling to estimate pre-retrofit energy use for seven projects for which 

measured data were not available. Post-retrofit energy-use data were obtained for 29 of the DER 

projects. Post-retrofit energy use was analyzed based on the net energy used by the DER project 

regardless of whether the energy was generated on site or delivered to the site. Homeowner 

surveys were returned by 12 of the pilot participants. 

Post-retrofit energy use data are analyzed with the objective of learning what post-retrofit energy 

performance one can expect from implementation of the retrofit package. In other words, the 

focus of the study was to project where a DER project will “end up” rather than to project the 

savings that any one project might realize.

All but two of the comprehensive DER projects achieved household source energy use below the 

Energy Information Administration Northeast regional household average. The mean for the 

group is 107.2 MMBtu/year, or approximately 38% below the regional household average. In 

terms of site energy use intensity (EUI), all of the projects perform below the regional average, 

with the mean values for both the multifamily and single-family DER projects below 50% of the 

respective Northeast region average. Two of the multifamily projects and three of the singlefamily projects meet the 2015 site EUI goal for the Architecture 2030 Challenge (Architecture 

2030 2006) without taking any credit for on-site electricity generation. 

Based on the experience of this sample of DER projects, this DER package is expected to result 

in yearly source energy use on the order of 110 MMBtu/year for a typical home. This is 

approximately 40% below the Northeast regional average for household energy use. Larger and

medium-sized homes that successfully implement these retrofits can be expected to achieve 

source EUI that is comparable to Passive House program targets for new construction.

All full DER projects achieved better than 50% reduction in total CFM50; all partial DER projects 

achieved better than 40% reduction in total CFM50. More than half of the full DER projects

achieved post-retrofit ACH 50 results below 1.5 ACH50. Some variations in airtightness 

performance are noted to accompany variations in DER implementation approach. For example, 

the group of DER projects that included the basement in the air control enclosure had a better 
x 

overall airtightness result than the group that excluded the basement (i.e., insulation and air 

control at basement ceiling). Also, the group of DER projects with unvented attics had a better 

overall airtightness result than the group with vented attics. 

In this group of DER projects, the reported energy-related portion of project costs ranged from 

slightly more than $31,500 to approximately $194,350. The reported energy-related costs 

averaged $34.59/ft2 (post-retrofit conditioned floor area) for the sample of DER projects. Noted 

variations in heating, ventilation, and air conditioning measure costs appear to relate to 

homeowner preferences, and do not appear to be correlated with a noticeable difference in 

performance (with the possible exception of one project that installed a ground source heat pump). 

Projects in this group of DER projects implemented three different approaches for attic/roof 

retrofit. The reported energy-related cost for a vented attic approach with insulation at the attic 

floor averaged $8.40/ft2. The unvented attic approach with rafter cavity insulation averaged only 

$11.59/ft2

. The unvented attic with insulation both exterior to the roof sheathing and between roof 

framing averaged $14.21/ft2. Excluding some noted outliers, the reported energy-related cost for 

the most typical wall retrofit approach ranged from $4.67/ft2 to $19.15/ft2 with an average of 

$10.51/ft2. 
1 

1 Introduction

The U.S. housing stock accounts for a significant portion of national energy usage. The volume of 

existing housing (approximately 130 million housing units) relative to the rate of housing unit 

construction (between approximately 500,000 and 2 million per year in recent years) makes 

energy performance retrofit absolutely essential to goals of reducing the energy use of the 

residential sector. 

Home retrofits have been targeted as an area of great potential for significant energy savings, 

employment opportunities, and market growth. Typical residential retrofit activity aims at 

mitigating performance liabilities of existing housing (NJIT 2013). High performance retrofit 

techniques are aimed at improving the performance of existing building components or whole 

buildings to equal or surpass current high performance new construction practices. 

Barriers to widespread adoption of high performance retrofit strategies remain high. Knowledge, 

skill, and even availability of building products represent persistent supply-side barriers to high 

performance retrofit. Vigorous market demand for high performance retrofit would provide the 

impetus for these barriers to fall. Two factors that constrain the market demand for high 

performance retrofit are: (1) the lack of confidence in or a lack of appreciation for the benefits of 

high performance retrofit; and (2) perceptions relative to the high cost of a comprehensive energy 

retrofit. 

Some in the industry have asserted that better modeling tools and methods are needed to predict 

savings resulting from retrofit measures.1 Clearly, a large body of evidence from actual retrofit 

projects is also needed to demonstrate the benefits and reveal the costs. 

This project reports the measured energy performance, airtightness and costs for 42 high 

performance residential retrofit projects. The projects are all participants in a National Gridsponsored deep energy retrofit (DER) pilot program. The projects implemented a consistent 

package of measures according to the requirements of this pilot program. Variations in the method 

of implementing measures as well as variations permitted in the overall package provide 

opportunities to investigate apparent impacts of these variations. 

The evaluation of retrofit performance focuses on the level of performance (in terms of energy use 

and airtightness) achieved rather than on reductions relative to pre-retrofit conditions. In other 

words, the analysis aspires to provide an idea of where a DER project implementing a similar 

package of measures is likely to “end up,” in terms of energy performance and airtightness. This 

is afforded by the comprehensive nature of the retrofits and by the measured post-retrofit 

performance. This approach sidesteps the complication of characterizing the pre-retrofit existing 

conditions. Relative savings projections are hugely dependent upon accurate characterization of 

existing conditions. Existing conditions in residential buildings are hugely variable and difficult to 

define for a project that is not known. By seeking to identify and describe a relatively consistent 

level of performance achieved through a package of measures, the project is able to project the 

results of high performance retrofit in a way that is much more stable and more widely applicable 

than savings projections. In other words, an understanding of the level of performance attained 

 

1 McIlvaine, et al. 2013 and Neymark and Roberts as discussed in Aspen Publishing 2013.
2 

through application of a package of measures allows one to project the savings achieved for a 

particular home with better certainty. One has only to compare the measured performance (or 

history) of the home in it its pre-retrofit state to the expected performance. Quantifying savings 

achieved for a package of retrofit measures is of limited value, as the savings would be repeatable 

only for homes that not only implement the same package of measures, but also have a similar 

pre-retrofit situation.

As participants in the DER pilot program, these retrofit projects all used the same set of enclosure 

performance targets, taken here as a “package of measures.” This report assesses the effectiveness 

of the overall package of measures as well as the relationship between different implementation 

strategies used and measures of performance. This is accomplished by analyzing the full set of 

performance data for the group rather than looking at individual case studies. This approach 

results in post-retrofit energy use and cost ranges based on the total community data that can be 

reasonably projected to other implementations of the DER package. The resulting energy use and

airtightness projections as well as cost ranges constitute concrete evidence that can be used by 

homeowners to assess the potential benefit and cost of a DER. 

This study does not include an analysis of retrofit package and measure costs relative to various 

effects sought from the measures. An analysis of cost and effect for some of the early completed 

projects in this pilot is included in a previous study (Gates and Neuhauser 2013). This earlier 

study found that non-energy benefits were either primary or significant motivations for a 

substantial portion of DER project expenditures. This finding highlights the importance of 

defining the “effect” whenever “cost effectiveness” is evaluated or discussed. The study also 

points to the need to acknowledge and value the range of desired effects obtained through a 

measure.

While the relative site energy savings from pre-retrofit to post-retrofit conditions ranges widely 

for this project—from 28% to 90%—the level of energy performance achieved is much more 

consistent. For the 27 comprehensive retrofit projects for which sufficient post-retrofit energy use 

data are available, the median and mean post-retrofit annual site energy use per household is 

slightly less than 50% of the regional average. The measured site energy use is within 20% of the 

mean for slightly fewer than half of the projects. 

The results of the pilot demonstrate that a relatively consistent level of performance can be 

achieved. But perhaps more importantly, the results demonstrate that the DER retrofits can meet 

energy performance goals and benchmarks representative of best-in-class new home construction. 
3 

2 Background

2.1 New Construction, Retrofits, and DERs

There are a substantial number of existing homes in the United States. The U.S. Census Bureau 

estimates that there were more than 130 million housing units in the United States in 2011 (U.S. 

Census Bureau 2013). This compares to typical new home construction rate of between 

approximately 500,000 and 2 million per year. In the years between 2007 and 2011, the 

construction industry added 3.1 million homes. The rate of new home construction relative to 

existing housing stock tells us that the majority of houses are likely to remain more than three 

decades old for some time to come. The rate also indicates that even super-efficient new 

construction will have a very limited impact on the overall energy use of the housing sector. 

Figure 1. U.S. housing units by decade of construction 

(U.S. Census Bureau, Annual Housing Survey data)

Until recent years, the primary focus of the Building America (BA) program has been research 

and development of techniques for new construction. The near-term goal of the BA program for 

new construction homes is to reduce energy use in new construction homes by 30% relative to a 

baseline established by the 2009 International Residential Code (Bianci 2011). The program has 

already succeeded in demonstrating performance packages achieving savings of 30%–50% 

relative to the baseline. Despite the impressive level of savings demonstrated for these packages, 

the new home packages represent a modest potential impact on national energy use due to the 

small percentage of new homes added to the aggregate national housing stock every year. 

Retrofit packages can be applied to a substantially greater portion of the U.S. housing stock than 

to new construction packages. The BA program near-term goal for the existing homes is to reduce 

energy consumption by 30% relative to the current condition of the existing home. For many 

existing homes, a 30% reduction in energy consumption will not be enough to elevate the 

performance to a level comparable to current standard practice (as defined by 2009 International 

Residential Code, for example). But at current rates of construction/replacement, it will take an 

extremely long time to replace the current housing stock with housing built to modern 
4 

performance standards. Even if rapid replacement were possible, retiring and replacing a 

significant portion of existing housing with high performance housing is not a reasonable 

proposition. Doing so would represent an unreasonable displacement and disruption of 

population, abandonment of physical and cultural resources embodied in existing buildings, and 

astronomical financial cost.

Obviously, reducing—by any significant measure—the energy use of the residential sector will 

require retrofitting existing housing. The DER pilot sponsored by National Grid provides an 

opportunity to assess whether a repeatable advanced retrofit package can elevate performance 

beyond that of typical new construction. The pilot also allows evaluation of the cost of achieving 

this level of performance through retrofit. 

2.2 Previous Work

The BA program has been working to overcome the obstacles associated with DERs. There are 

several other BA teams evaluating the performance effectiveness of cold climate home retrofit 

approaches at the community scale. They include the Consortium for Advanced Residential 

Buildings’ role in the Retrofit NYC Block by Block project (Eisenberg et al. 2012) and in the 

recently completed retrofit of the Chamberlain Heights duplex and quad affordable housing 

complex (Donnelly and Mahle 2012) as well as the Partnership for Advanced Residential 

Retrofits team’s work in the Chicagoland project development of energy efficiency retrofit 

packages for typical houses in the Chicago area (Spanier et al. 2012).

These research projects have the potential to provide a significant set of post-retrofit performance 

data using utility bills and other testing to evaluate the energy use level achieved (and achievable) 

by fairly comprehensive retrofit measure packages. However, the current reports have only 

limited results available (if any), and most results are presented in terms of software models rather 

than actual performance data. In this current research project, Building Science Corporation 

(BSC) is making use of a year of post-retrofit utility bills and performance data for retrofit 

projects. BSC then uses this actual performance information to project achievable performance 

levels for the DER retrofit measure package. 

The Consortium for Advanced Residential Buildings and Partnership for Advanced Residential 

Retrofits research projects adopt the approach of tailoring retrofit measure packages to particular 

house types—e.g., ranch house, NYC row house, or triple-decker. In contrast, BSC has found that 

each retrofit project has its own set of unique constraints that are based not so much on house type 

and age as on its history and existing conditions. Therefore, tailoring retrofit measure packages to 

specific house types may not be necessary. In the results described in the current report, a single 

DER measure package has been applied to a variety of housing types, as well as across

significantly different ages and existing conditions. 

Other previous work related to high performance retrofit has focused on individual components or 

measures. For example, in one recent BA project, BSC worked with a weatherization program to 

evaluate and develop plans for inclusion of roof or attic insulation in the weatherization program 

(Neuhauser 2012). The current study evaluates the impact of a comprehensive measure package. 
5 

2.3 Building Science Corporation and the National Grid DER Pilot Program

BSC has conducted several research projects using information, data, and experiences from 

retrofit projects participating in the National Grid DER pilot program. In one project, BSC 

performed a case-by-case evaluation of the implementation of the DER measures for five of the 

DER pilot program participants (Neuhauser 2011). In a second project, BSC looked at the preand post-retrofit performance data for seven DER projects, four of which were early participants 

in the DER pilot program (Osser et al. 2012). 

The thrust of these earlier research projects dealt with the individual projects—either in terms of 

how the DER measures were implemented or the post-retrofit performance that each one 

achieved. None of them compared and analyzed the performance data as a group. Now that 

additional projects have been completed in the National Grid DER pilot program, there are 

enough data available to warrant the analysis of all of these projects as a community of retrofits 

rather than as individual cases. The number of completed projects is large enough that the impact 

of the retrofit measures as a package can be analyzed, and trends from the available data about 

these projects begin to emerge. Using this approach, the emphasis is shifted from the post-retrofit 

performance for the individual case to the post-retrofit performance achievable by using the DER 

package.

As the designated technical support provider to the National Grid DER pilot program since its 

inception in 2009, BSC has had the opportunity to learn from more than 40 residential DER

projects. BSC, in its role as the technical support team, provided technical review of project plans 

for all projects participating in the pilot program, and conducted in-field review and verification 

of measures for most of the projects. BSC also contributed to pilot program design and 

implementation. A significant portion of BSC’s involvement with the National Grid DER pilot 

program was supported through the BA program.

Four DER projects were completed through the pilot program in 2010. Eleven DER projects 

reached completion in 2011. By the close of the pilot program in December 2012, 42 projects had 

been successfully implemented through the program. 

The individual projects participating in the pilot program have adhered to a common basic outline 

of target building enclosure performance. Project teams devised a variety of approaches to meet 

these targets. Particular conditions and configurations of the existing buildings resulted in a 

variety of implemented methods and ways of addressing challenges. 

Under a previous task order, BSC produced a review of methods employed and challenges faced 

by the early program participants (Neuhauser 2011). Also under a previous task order, BSC 

analyzed performance data for a sample of homes for which the DER project was completed or 

substantially completed prior to the last year of the program (Gates and Neuhauser 2013). 

Now, with 42 DER projects representing approximately 60 dwelling units complete at the 

December 2012 close of the pilot, BSC has seized upon a unique opportunity to analyze 

performance data for a large population of DER projects. Studying this population of DER 

projects also reveals successful approaches for common retrofit challenges.
6 

3 National Grid Deep Energy Retrofit Pilot Program

The National Grid DER pilot program was launched in 2009 with the goal of demonstrating 

advanced comprehensive retrofit and evaluating the viability of such retrofits as the target of a 

large-scale energy efficiency program. The performance aspiration in the pilot was to achieve 

50% energy reductions compared to a typical home in the region (National Grid 2009). 

In order to protect the interests of its customers National Grid insisted that energy efficiency 

measures implemented through the program would also support building durability and indoor 

environmental quality. National Grid partnered with BSC as a technical support team to help 

ensure that the measures supported through the program are effective and that “The project plan 

and implementation... demonstrate sound building physics as it relates to moisture management 

of the enclosure and effectiveness of the mechanical system configuration” (National Grid 2011). 

The program offers significant financial incentives. Incentives are intended to offset a portion of 

net incremental costs specifically related to energy performance measures. Base incentive limits 

for one- and two-family dwellings are indexed to conditioned floor area of the building and range 

from $35,000 to $42,000 for detached single-family residences and $50,000 to $60,000 for 

duplexes. The incentive offered to multifamily buildings of three units or more varies according to 

the number of units in the building. The base incentive for the three-family building is $72,000 

and for a building with 10 or more units, the base program incentive is $106,000. 

The program was open to residential ratepayers and building owners within National Grid’s 

Massachusetts and, later, Rhode Island service territory. Projects were accepted into the pilot 

program after successfully completing an in-depth application and review process. 

3.1 Measures and Targets

The DER homes included in this report are all of those that successfully completed the National 

Grid DER pilot program.2 Participants in the DER pilot program are required to meet: 

• Health, safety, and indoor air quality guidelines 

• Specific thermal targets for each enclosure component (e.g., roof, above-grade walls) 

• An overall airtightness target 

• Minimum efficiency of mechanical equipment

• Water management and durability requirements. 

While there are not specific instructions for how these targets are to be met, all implementation 

plans are reviewed for sound building science before the project is accepted into the pilot 

program. After the review, field verification of each completed measure is required in order to 

receive the financial incentives. In addition, all project teams must include a qualified contractor 

or design consultant with previous DER experience and approval by National Grid. 

 

2 Analysis of post-retrofit energy performance is limited to those projects that were also occupied by January 2013 

and for which sufficient post-retrofit energy use data were made available to BSC. 
7 

Implementation of a DER will change the behavior of existing building systems, including effects 

of airtightness and reduced heat flow through assemblies. The measures shown in Table 1 include 

some essential prerequisites put in place to address possible ramifications of those changes. 

Table 1. Overall Measures and Targets or Requirements for National Grid DER Pilot Retrofit 

Measure Target or Requirement 

for Measure

Project Implications and 

Practices Followed

Combustion 

Safety

Requirement: No atmospherically 

vented combustion appliances or 

fireplaces

Projects used direct vent, closed 

combustion, or power-vented mechanical 

equipment

Indoor Air 

Quality

Requirement: Meet ASHRAE 

62.2 ventilation requirements 

Provide background ventilation system 

with sufficient capacity and easily 

accessible controls that allow residents to 

adjust the ventilation rate according to 

occupant needs.

Durability

Requirement: Robust water 

management and vapor control 

required of the retrofit enclosure

system

Use appropriate flashings (including step 

and kickout flashings); integrate flashings 

effectively into the water control layer; 

ensure that vapor control methods do not 

trap moisture within building components

Air 

Infiltration

Control 

Target: CFM50 ≤ 0.10 * total 

6-side enclosure surface area (ft2) 

Identify the air control layer for each 

enclosure component and indicate how 

the air control function is transitioned 

between components

Appliances 

and Lighting

Target: ENERGY STAR®

appliances; 90% of lighting to be 

compact fluorescent or better

Incentives and provision of energyefficient lighting facilitated by National 

Grid

The enclosure targets, shown in Table 2, are given for each enclosure component and are in terms 

of the installed R-value of insulation; the targets are consistent with Straube (2011). 

Table 2. Enclosure Insulation Measures and Targets for National Grid DER Pilot Retrofit 

Measure Target for 

Measure Comments

Roof R-60+ For unvented attics

Attic R-60+ For a vented attics

Above-Grade Exterior Walls R-40+

Insulated Foundation Walls R-20+ For walls that are below or 

partially below grade

Insulated Basement Floor R-10+

Basement Ceiling R-30+ Applies only if the basement is not 

included in the thermal enclosure

Floor Over Unheated Garage or Overhang R-40+

Windows and Doors R-5+
8 

This set of enclosure measures allows the project to choose between a vented or unvented attic, 

and between insulated basement walls or an insulated basement ceiling. In addition, some projects 

were unable to provide insulation to the basement floor because of head height or structural 

constraints. This type of flexibility of measures is necessary when working with retrofits, as

existing conditions may preclude certain approaches. 

The heating, ventilation, and air conditioning (HVAC) measures are shown in Table 3. 

Table 3. HVAC Measures and Targets for National Grid DER Pilot Retrofit 

Measure Target for 

Measure Comments

Mechanical Ventilation

Heat recovery, 

balanced, 

distributed

HRVa, ERVb, exhaust only, or supply only are 

acceptable provided ASHRAE 62.2 is met and 

there is a means of distribution; mechanicals and 

ductwork to be within the thermal enclosure.

Heating Equipment High efficiency 

heating

Furnace, condensing boiler, GSHPsc or ASHPsd; 

AFUEe 95+%, heating season performance factor

8.2+ equipment rating with configuration or 

operating sequences to allow efficient operation; 

mechanicals and ductwork to be within the 

thermal enclosure.

Cooling Equipment

16 seasonal 

energy 

efficiency ratio, 

13 energy 

efficiency ratio

Cooling is not required; air handling equipment 

and ductwork (if any) to be within the thermal 

enclosure. 

a Heat recovery ventilator

b Energy recovery ventilator

c Ground source heat pump

d Air source heat pump

e Annual fuel utilization efficiency

3.2 The Community of Retrofits

This report examines the airtightness and construction costs of 42 projects (representing 60 

housing units), all of which were participants in the National Grid DER pilot program. Therefore, 

all of the retrofits used the same DER measure package and targets in their planning; had plans 

reviewed for sound building science and for durability, combustion safety, and air quality; and 

received site verification of the DER measures. Of the 42 projects that successfully completed the 

National Grid DER pilot program, 37 are full DER projects and five are partial DER projects. In 

the following sections, the results of these projects are reported and analyzed in terms of energy 

use, airtightness, construction cost, and homeowner satisfaction. 

Table 4 and Table 5 provide some basic information about each of the completed retrofit projects 

that participated in the pilot. The tables also include information about the three enclosure 

components for which different implementation approaches were followed—roof and attic, 

above-grade walls, and basement. Additional information about the retrofit projects is provided in 

Section 4.1, Section 4.2, and Section 4.3.
9 

Table 4. DER Community—37 Comprehensive DERs

House Location Year 

Built

PreRetrofit 

Cond. 

Area 

(ft2)

PostRetrofit 

Cond. 

Area 

(ft2)

Roof/Attic 

Measure 

(Installed 

R-Value)

Above-Grade 

Walls Measure 

(Installed 

R-Value)

Basement 

Measure HVAC and DHW Measures

Belchertown, MA 1760 1,435 1,907 Below roof deck 

insulation only

Double wall with 

interior insulation

Existing porch 

roof/deck not 

detached

Foundation walls 

and slab 

insulated

HRV; propane furnace; tankless 

propane water heater; no air 

cooling

Belmont, MA 

(2 units) 1925 3,417 4,768

Exterior and below 

roof deck

insulation

Exterior and wall 

cavity insulation

Foundation walls 

insulated

HRV for each unit; gas furnace 

and central air conditioner for 

each unit; solar thermal water 

heating with electric backup

Millbury, MA 1953 1,868 1,868

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and slab 

insulated

Supply-only ventilation; minisplit ASHP for heating and 

cooling w/ two ducted air 

handlers; direct vent existing 

wood pellet stove for heating 

backup; tankless propane water 

heater

Milton, MA 1960 2,368 2,368 Below roof deck 

insulation only

Exterior and wall 

cavity insulation

Foundation walls 

and slab 

insulated

HRV; gas water heater with 

hydronic air handler for 

heating; central air conditioner

Quincy, MA 1905 3,484 4,567

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; solar thermal integrated 

with gas water heater for 

radiant heating and hot water; 

ASHP for heating and cooling

Arlington, MA

(2 units) 1910 2,502 3,627 Below roof deck 

insulation only

Exterior and 

cavity insulation

Existing porch 

roof/deck not 

detached

Basement ceiling 

insulated

HRV for each unit; condensing 

gas furnace for each unit; 

central air conditioner for upper 

unit; tankless gas water heater 

for each unit
10 

House Location Year 

Built

PreRetrofit 

Cond. 

Area 

(ft2)

PostRetrofit 

Cond. 

Area 

(ft2)

Roof/Attic 

Measure 

(Installed 

R-Value)

Above-Grade 

Walls Measure 

(Installed 

R-Value)

Basement 

Measure HVAC and DHW Measures

Newton, MA 1930 1,815 2,199

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Existing porch 

roof/deck not 

detached

Foundation walls 

and floor slab 

insulated

ERV; condensing gas boiler for 

heating and indirect water 

heating; ASHP for cooling and 

shoulder season heating

Jamaica Plain-A, 

MA

(3 units)

1907 3,885 3,885

Vented attic with 

attic floor 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV for each unit; existing gas 

boiler for heating and indirect 

water heating; removable 

window air conditioners

Northampton-A, 

MA 1859 2,032 2,747

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

ERV; GSHP; mini-split ASHP 

for upper floor office; ASHP 

water heater

Lancaster-A, MA 1900 980 1,440

Vented attic with 

attic floor 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

ERV; two mini-split ASHPs (1 

head each); tankless gas water 

heater

Brookline, MA 1899 3,174 3,174

Previous retrofit 

phase: below roof 

deck insulation 

only to R-48

Exterior and wall 

cavity insulation

Foundation walls 

insulated

HRV; gas boiler with indirect 

water heating; no air cooling

Westford, MA 1993 2,906 3,955 Below roof deck 

insulation only

Exterior and wall 

cavity insulation

Foundation walls 

insulated

ERV; existing gas furnace; 

central air conditioner; gas 

water heater

Gloucester, MA 1920 2,171 2,424

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; two mini-split ASHPs 

(one with 2 heads, the other 

with 3 heads–2 of which are 

ducted) with backup electric 

resistance heat; solar thermal 

water heating with electric 

backup
11 

House Location Year 

Built

PreRetrofit 

Cond. 

Area 

(ft2)

PostRetrofit 

Cond. 

Area 

(ft2)

Roof/Attic 

Measure 

(Installed 

R-Value)

Above-Grade 

Walls Measure 

(Installed 

R-Value)

Basement 

Measure HVAC and DHW Measures

Medford, MA

(2 units) 1916 3,200 3,200

Vented attic with 

attic floor 

insulation

Exterior and

wall cavity 

insulation

Existing porch 

roof/deck not 

detached

Basement ceiling

insulated

HRV for each unit; gas water 

heater (integrated with solar 

thermal) for each unit with 

hydronic air handler; central air 

conditioner

Northampton-B, 

MA 1972 1,126 2,209

Vented attic with 

attic floor 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

insulated

Exhaust only ventilation; gas 

boiler for heating and indirect 

water heating; no air cooling

Haverhill, MA

(2 units) 1900 1,542 2,542

Exterior and below 

roof deck 

insulation

non-chainsaw

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV for each unit; mini-split 

ASHP (1 head) for heating and 

cooling for each unit; solar 

thermal water heating with 

electric backup

Dorchester, MA

(3 units) 1880 4,200 4,200

Vented attic with 

attic floor 

insulation

and roof with 

insulation below 

roof deck

Exterior and wall 

cavity insulation

Existing porch 

roof/deck not 

detached

Basement ceiling 

insulated

ERV for each unit; gas furnace 

and central air conditioner for 

each unit; tankless gas water 

heater for each unit

Rutland, MA 1977 1,415 2,720

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; propane boiler for 

heating and indirect water 

heating; no air cooling

Methuen, MA 1940 767 1,528

Vented attic with 

attic floor 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

insulated

HRV; mini-split ASHP (3 

heads) for heating and cooling; 

solar thermal water heating with 

electric backup

Wakefield, RI 1979 2,200 2,873

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; existing propane boiler 

for heating; ASHP water heater; 

2 existing mini-split air 

conditioners
12 

House Location Year 

Built

PreRetrofit 

Cond. 

Area 

(ft2)

PostRetrofit 

Cond. 

Area 

(ft2)

Roof/Attic 

Measure 

(Installed 

R-Value)

Above-Grade 

Walls Measure 

(Installed 

R-Value)

Basement 

Measure HVAC and DHW Measures

Groton, MA 1961 2,222 3,547

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; gas boiler for heating and 

indirect water heating; 

removable window air 

conditioner

Williamstown, 

MA 1940 759 1,827

Vented attic with 

attic floor 

insulation

Exterior and wall 

cavity insulation

Existing deck and 

porch roof not 

detached

Foundation walls 

and floor slab 

insulated

HRV; gas boiler for heating and 

indirect water heating; no air 

cooling

North Kingstown, 

RI

(2 units)

1962 3,520 3,520 Below roof deck 

insulation only

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV for each unit; mini-split 

ASHP (2 heads) for heating and 

cooling for each unit; tankless 

gas water heater for each unit

Cohasset, MA 1983 2,050 4,380

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; propane furnace for 

heating; central air conditioner; 

propane water heater

Sudbury, MA 1960 1,670 3,054

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; gas boiler for heating and 

indirect water heating; minisplit air conditioner (4 heads)

Worcester, MA 

(3 units) 1890 2,100 2,240

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV for each unit; mini-split 

ASHP (1 head) for heating and 

cooling for each unit; tankless 

gas water heater for each unit

Northampton-C, 

MA 1900 1,284 2,201

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

insulated

HRV; existing gas boiler for 

heating and indirect water 

heating; no air cooling

Warwick, MA 1979 1,196 2,033

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; mini-split ASHP (1 head) 

for heating and cooling; solar 

thermal water heating with 

electric backup (also provides 

backup heating)
13 

House Location Year 

Built

PreRetrofit 

Cond. 

Area 

(ft2)

PostRetrofit 

Cond. 

Area 

(ft2)

Roof/Attic 

Measure 

(Installed 

R-Value)

Above-Grade 

Walls Measure 

(Installed 

R-Value)

Basement 

Measure HVAC and DHW Measures

Lexington, MA 1946 1,979 2,791 Below roof deck 

insulation only

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; gas furnace; no air 

cooling; gas water heater

Melrose, MA 1945 2,150 2,706

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; mini-split ASHP (2 

heads) for heating and cooling; 

ASHP water heater

Providence-A, RI

(3 units) 1915 4,449 4,449 Below roof deck 

insulation only

Exterior and wall 

cavity insulation

Basement ceiling 

insulated

HRV per unit; gas boiler per 

unit and indirect water heating; 

electric resistance heating in 

common areas; through wall air 

conditioners

Roslindale, MA 1865 2,165 2,685

Exterior and below 

roof deck 

insulation

partial chainsaw

Exterior and wall 

cavity insulation

Foundation walls 

insulated

HRV; existing gas boiler plus 

electric resistant heating in 

bath; solar thermal water 

heating with existing gas water 

heater backup

Lowell, MA 1924 1,336 2,501 Exterior insulation

partial chainsaw

Exterior and wall 

cavity insulation

Foundation walls 

and part of floor 

slab insulated

HRV; existing gas boiler with 

radiant heat and indirect water 

heating; no air cooling

Waltham, MA 1960 1,240 2,010

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

HRV; gas furnace; tankless gas 

water heater; central air 

conditioner

Northampton-D, 

MA

(2 units)

1900 4,784 4,784

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

Unit 1: ERV; mini-split ASHP 

(1 head) for heating and 

cooling; electric water heater.

Unit 2: 2 ERVs; mini-split 

ASHP (3 heads) for heating and 

cooling; electric water heater
14 

House Location Year 

Built

PreRetrofit 

Cond. 

Area 

(ft2)

PostRetrofit 

Cond. 

Area 

(ft2)

Roof/Attic 

Measure 

(Installed 

R-Value)

Above-Grade 

Walls Measure 

(Installed 

R-Value)

Basement 

Measure HVAC and DHW Measures

Lancaster-B, MA

(2 units) 1986 3,172 3,792

Exterior and below 

roof deck 

insulation

Exterior and wall 

cavity insulation

Foundation walls 

and floor slab 

insulated

Unit 1: 2 HRVs; two mini-split 

ASHPs for heating and cooling; 

tankless propane water heater.

Unit 2: 1 HRV; existing 

propane boiler for heating and 

indirect water heating; minisplit ASHP for cooling

Providence-B, RI 

(3 units) 1930 3,054 3,054 Below roof deck 

insulation only

Exterior and wall 

cavity insulation

Basement ceiling 

insulated

HRV per unit; gas boiler per 

unit (located in unconditioned 

basement) for heating and 

indirect water heating; electric 

resistance heating in common 

areas; through-wall air 

conditioners
15 

Table 5. DER Community—5 Partial DERs

House 

Location 

Year 

Built

PreRetrofit 

Cond. 

Area 

(ft2

) 

PostRetrofit 

Cond. 

Area 

(ft2

) 

Roof/Attic 

Measure 

(Installed 

R-Value)

Above-Grade 

Walls Measure

(Installed 

R-Value)

Basement 

Measure HVAC and DHW Measures

Jamaica 

Plain-B, MA

187

8 5,663 5,663

Below roof 

deck insulation 

only

n/a

Foundation 

walls and 

floor slab 

insulated

Supply-only ventilation; existing

gas boiler with hydronic air 

handlers and indirect water 

heating; existing central air 

conditioning

Florence, MA 188

0 2,690 3,976

Vented attic 

with attic floor 

insulation

n/a

Foundation 

walls and 

floor slab 

insulated

HRV; gas boiler for heating and 

indirect water heating; direct vent 

wood stove; no air cooling

Concord, MA 195

6 3,620 3,620

Exterior and 

below roof 

deck insulation

partial 

chainsaw

n/a n/a

Exhaust-only ventilation; existing 

gas boiler for heating and indirect 

water heating; 2 existing mini-split 

air conditioners

Watertown, 

MA

(2 units)

192

8 2,645 2,899

Exterior and 

below roof 

deck insulation

chainsaw

n/a

Foundation 

walls and 

floor slab 

insulated

Lower unit: existing gas furnace 

and gas water heater. Upper unit: 

HRV; mini-split ASHP for heating 

and cooling; tankless gas water 

heater

Jamaica 

Plain-C, MA 

(3 units)

191

8 3,748 3,748

Exterior and 

below roof 

deck insulation

no chainsaw 

(internal drain 

low slope roof)

n/a n/a

Exhaust only ventilation; central 

gas water heater and hydronic air 

handler for each unit
16 

In the “Roof/Attic Measure” column of Table 4 and Table 5, some DER projects are identified as 

using the “chainsaw” technique. This refers to a retrofit technique used at the intersection of the 

roof and exterior wall whereby the existing rafter tails and rake overhangs are cut off during the 

retrofit and new overhangs are built and attached at completion (Orr and Dumont 1987; Holladay 

2009). This approach is often used in a DER when exterior insulation is to be applied to both the 

roof and the wall, since it allows a continuous layer of insulation to be applied across the 

intersection, thus reducing thermal bridging. More importantly, it simplifies the air control 

connection between the roof and the wall when the air control layers for both the roof and the wall 

are on the outside of the existing sheathing, since the intersection becomes a simple edge 

condition.

In the “Above-Grade Walls Measure” column of Table 4 and Table 5, there is a note “existing 

porch roof/deck not detached” for some of the projects. When exterior insulating sheathing is used 

on the above-grade walls for a DER, it is recommended that any porches or decks that are 

attached to the above-grade wall (i.e., not integral to the structure of the building) be temporarily 

detached during the retrofit so that the air control layer and the insulation can be applied 

continuously between the porch or deck and the wall. This note indicates that the project did not 

use this approach.

It is clear from Table 4 and Table 5 that the teams implemented retrofit measures in several ways. 

Key variations are summarized below:3

• Variation in above-grade wall treatment:

o One project used interior insulation only (a new stud wall was built around the 

interior perimeter to create a deeper cavity for insulation).

o Thirty-six projects applied insulation to the exterior of the existing walls. 

o Of the 36 projects that applied insulation to the exterior, eight also used spray 

polyurethane foam insulation in the wall cavities.

• Variation in roof and attic treatment:

o Eight projects used a vented attic with insulation on the attic floor and intentional 

ventilation openings. 

o Eleven projects created an unvented attic with all of the required insulation below 

the existing roof sheathing. 

o Twenty-four projects created an unvented attic using insulation applied over the 

existing roof sheathing; 

 Nineteen of these projects used the “chainsaw” technique. 

 Three implemented significant elements of the “chainsaw” technique. 

 One project involved a wood-framed sloped roof and did not implement 

any elements of the “chainsaw” technique. 

 

3 Note that the number for each variation under the major components does not sum to the total number of projects 

in the study because the study includes partial DER projects that did not treat each of these components.
17 

 One project involved an unvented attic beneath a low-sloped roof of a 

building with masonry parapets. 

• Variation in basement treatment: 

o Five projects insulated the basement ceiling rather than the basement walls.

o Seven projects insulated the basement walls but did not insulate the basement 

floor.

o Twenty-eight projects insulated the basement walls and the basement floor.

As participants in the DER pilot program, all of these DER projects provided data in the 

application forms, had pre- and post-retrofit blower door testing performed, and are contractually 

obligated to provide energy use information for at least the first 2 years following completion of 

the DER. Data from the application form include facts about the house, information on existing 

conditions, past energy use, performance concerns, existing R-values, as well as descriptions of 

plans for implementing the measures and projected costs. This, together with on-site verification 

of the DER project measures, provided a consistent set of data about each retrofit analyzed in this 

research report. 
18 

4 Energy Use Results and Analysis 

A key goal of the National Grid DER pilot project was to demonstrate that energy use reduction 

of 50% or more relative to typical homes could be achieved through enclosure upgrades and 

efficiency upgrades to mechanical equipment. To meet that goal, the program used aggressive 

performance targets for retrofit of enclosure components (see Table 2). These thermal enclosure 

specifications, together with improved airtightness, were expected to reduce heating and cooling 

loads significantly. In addition, participants were encouraged to replace old equipment—

appliances, HVAC equipment, and lighting—with energy-efficient equipment (see Table 3). In 

the case of HVAC equipment, this provided opportunity for right-sizing the equipment to better 

match the reduced heating and cooling loads. The major leverage of the pilot program, therefore, 

related to heating and cooling energy use. The program also encouraged reduction of lighting 

energy use by providing free or reduced-cost efficient lamps and lighting fixtures. The program 

documentation also required that major appliances in the retrofit homes be ENERGY STAR

qualified. Other major end uses in the homes were outside of the purview of the program. 

4.1 Reduction Versus Performance Achieved

For retrofit measures aimed at reducing energy use (and primarily heating and cooling energy use) 

the relative energy use reduction that can be achieved for any one home reflects not only the 

effectiveness of the measures but also the pre-retrofit state of the building and how the building is 

used by its occupants. The pre-retrofit energy use is highly variable between different homes. 

Because occupant behavior and building pre-retrofit conditions have a determining effect on the 

apparent relative savings associated with a retrofit measure, the apparent reductions or “savings” 

associated with a measure are difficult to translate from one house/household to another without 

knowing a significant amount of information about each. 

Further muddying the relationship between energy use reduction and retrofit measures is that a 

retrofit project is often combined with other home improvements that result in a change in the size 

of the home (usable conditioned floor area). 

Although thorough characterization of the pre-retrofit condition and meticulous “tuning” of 

energy models may allow for translation of savings projections from one building to another, this 

work diverts resources from the retrofit itself. Extensive modeling of the pre-retrofit condition

may be of limited value when the performance resulting from a comprehensive package can be 

projected with reasonable certainty. With a projection of the resulting performance, the relative 

savings or reduction can be calculated by comparing current use to the expected post-retrofit 

performance. 

In this section, the post-retrofit energy use of the group of DER projects is analyzed to assess the 

level of energy performance achieved by the retrofit package implemented in the National Grid 

DER pilot. The level of energy performance achieved is compared to energy performance 

benchmarks. Energy performance of the group of DER projects is also analyzed to assess whether 

different implementation strategies have significant energy performance implications. While 

projection of post-retrofit energy use resulting from implementation of the package might be more 

stable and more readily generalized than relative savings, it is important to note that measured 

post-retrofit energy use is also subject to highly variable occupant behavior and other operating 

conditions. 
19 

4.2 Site and Source Energy

Energy performance can be shown as site or source (or “primary”) energy. Looking at site energy 

allows an analysis of energy consumption directly in the house; at this level, homeowners can 

precisely measure energy consumption using meters or monitors. On the other hand, in order to 

appropriately assess the environmental impact and total energy consumption of the home’s energy 

use (including production and transport of the fuel or electricity), source energy use is the vital 

metric. In addition, source energy is typically comparable to the energy cost for the end user 

(Ueno and Straube 2010). The analysis presented in this report considers both source energy and 

site energy use. 

Source energy use is calculated using the source to site energy conversion factors shown in Table 

6 (nationwide averages from EPA 2011). The total site and source energy use reported in Table 7 

presumes that all electricity was from the grid. 

Table 6. Source-Site Ratios for All Portfolio Manager Fuels 

(EPA 2011)

Fuel Type Source-Site Ratio

Electricity (Grid Purchase) 3.34

Natural Gas 1.047

Fuel Oil (1, 2, 4, 5, 6, Diesel, Kerosene) 1.01

Propane and Liquid Propane 1.01

Wood 1.0

4.3 On-Site Generation

Eleven of the houses in this retrofit community generate some electricity on site through 

photovoltaic installations. While the electricity produced by these systems can offset some or all 

of the energy that the building would otherwise need to import from the grid, in this study, the onsite generation facility is not a part of the package of measures evaluated. The aim of the research 

effort is to ascertain the level of performance achievable through a particular package of retrofit 

measures. Therefore electrical energy used by the DER projects in this study is the gross energy, 

and not the net energy, used by the building. 

4.4 Energy Use Data

The actual post-retrofit energy use data are derived from the monthly energy use reported by the 

electricity and gas utility companies, delivery amounts and dates for periodic delivery fuels (such 

as propane and wood pellets), and on-site electricity production data made available to BSC by 

the DER homeowners. The data were processed for use in the analysis by allocating energy use to 

calendar months so that monthly energy use could be associated with monthly weather data. In 

most cases, this involved adjusting the data relative to energy units used per day in the billing 

periods. In some cases, periodic delivery fuels, such as propane and wood pellets, had to be 

distributed according to daily use portions and weather-affected portions using daily weather data.

To have sufficient energy use data representative of expected operational conditions, the projects 

had to be completed (and back to full occupancy) by January of 2013. Data were collected for the 

entire post-retrofit period through July, August, or September of 2013. 
20 

For projects with on-site generation, determining the gross electricity usage of the house required 

monthly generation data as well as the net electricity supplied to/from the grid. The net electricity 

position with respect to the grid plus the monthly on-site generation yields the gross electric 

consumption of the home. Some utility bills do not indicate net electricity supplied to the grid: 

months with a net supply to the grid are represented as 0 kWh usage rather than showing a 

negative kilowatt-hour position. In some cases, the homeowner was able to provide the net 

electricity supply data. The DER program manager at National Grid was able to track down raw 

meter read data that helped determine the gross electrical energy use data for other projects. For 

some projects, it was not possible to determine the gross energy usage and, therefore, data for that 

project could not be included in the analysis. 

In all, BSC received sufficient post-retrofit energy usage data for 28 of the DER projects. For 

another project, a previous year of post-retrofit data provided suitable information. The energy use 

analysis in this report includes 29 of the DER pilot projects. Twenty-seven of these are 

comprehensive DER projects, two are partial (or “staged”) DER projects.4 In this section, “all 

DER projects” or “the entire group of DER projects” is used to refer to the entire group of projects 

for which adequate post-retrofit energy use data were available.

The pre-retrofit data are from monthly energy use data provided by the utility companies or 

provided by the homeowner on program application forms. Energy modeling was used to generate 

pre-retrofit usage when the building was not occupied by the current owners prior to the retrofit.

Table 7 and Table 8 summarize the pre-retrofit and post-retrofit energy use data, respectively, for 

the houses included in this section of the report.

 

4 Included among the comprehensive DER projects is one project that had implemented high performance retrofit 

for the roof and basement prior to participating in the National Grid program. Participation in the National Grid 

program resulted in a comprehensive retrofit for this home.
21 

Table 7. DER Community Pre-Retrofit Energy Use—12 Months

House Location 

Time Period or 

Energy Modeling 

Tool Used 

Primary 

Heating 

Fuel

Electricity 

(kWh)

Natural Gas 

(therm) or 

Propane (gal)

Fuel Oil 

(gal) 

Other 

Energy 

Source

Total Site 

Energy 

(MMBtu)

Total 

Source

Energy 

(MMBtu)

Belchertown, MA Jul 08–Jun 09 Wood 2,079 174 (P) 7 cords wood 195 211

Belmont, MA (2 units) BEopt v 2.0 Gas 9,273 322 (NG) 2,791 451 530 

Millbury, MA May 09–Apr 10 Oil 7,730 375 150, 40-lb 

bags pellets 125 187 

Milton, MA BEopt v 2.0 Gas 8,089 865 (NG) 114 183

Quincy, MA Jan 09–Dec 09 Oil 12,557 550 119 220 

Arlington, MA (2 units) BEopt v 2.0 Gas 9,059 2,852 (NG) 316 402 

Newton, MA Oct 09–Sep 10 Gas 7,639 1,222 (NG) 148 215 

Jamaica Plain-A, MA

(3 units) Aug 09–Jul 10 Gas 7,456 1,760 (NG) 201 269 

Northampton-A, MA Jan 09–Dec 09 Gas 4,443 1,164 (NG) 132 173 

Lancaster-A, MA BEopt v 2.0 Oil 5,677 668 112 158 

Brookline, MA Sep 09–Aug 10 Gas 3,284 773 (NG) 89 118 

Westford, MA Jan 10–Dec 10 Gas 9,763 1,761 (NG) 209 296

Gloucester, MA Jun 09–May 10 Oil 5,428 910 145 189 

Medford, MA (2 units) Jun 08–May 09 Gas 12,517 3,069 (NG) 350 464 

Northampton-B, MA BEopt v 2.0 Gas 5,756 832 (NG) 103 153 

Haverhill, MA (2 units) BEopt v 2.0 Oil 7,403 36 (NG) 943 160 220 

Rutland, MA Aug 08–Jul 10 Oil 10,443 58 (P) 465 0.3 cords 

wood 113 197 

Methuen, MA Dec 10–Nov 11 Oil 8,089 584 109 174 

Wakefield, RI Jan 11–Dec 11 Propane 9,573 754 (P) 102 179 

Groton, MA Jun 10–May 11 Oil 8,724 878 152 222

Cohasset, MA BEopt v 2.0 Oil 12,611 1,597 265 367 
22 

House Location 

Time Period or 

Energy Modeling 

Tool Used 

Primary 

Heating 

Fuel

Electricity 

(kWh)

Natural Gas 

(therm) or 

Propane (gal)

Fuel Oil 

(gal) 

Other 

Energy 

Source

Total Site 

Energy 

(MMBtu)

Total 

Source

Energy 

(MMBtu)

Sudbury, MA May 10–Apr 11 Oil 10,939 743 37 125 

Northampton-C, MA Aug 10–Jul 11 Gas 4,105 567 (NG) 71 106 

Warwick, MA Sep 10–Aug 11 Oil/wood 1,351 80 1.3 cords 

wood 48 58 

Melrose, MA Jan 11–Dec 11 Oil 6,012 227 (NG) 1,725 282 334

Lowell, MA Dec 10–Nov 11 Gas 6,757 558 (NG) 79 135 

Waltham, MA Nov 09–Oct 10 Gas 4,563 694 (NG) 85 125 

Jamaica Plain-B, MA May 09–Apr 10 Gas 7,059 2,499 (NG) 274 342 

Concord, MA Nov 10–Oct 11 Gas 14,265 1,815 (NG) 230 353 
23 

Table 8. DER Community Post-Retrofit Energy Use

House Location Time Period

Primary 

Heating 

Fuel

Electricity 

(kWh)

Natural Gas 

(therm) or 

Propane (gal)

Other Energy 

Source

Total Site 

Energy 

(MMBtu)

Total 

Source

Energy 

(MMBtu)

Belchertown, MA Aug 12–Jul 13 Propane 1,916 362 (P) 40 55 

Belmont, MA (2 units) Aug 12–Jul 13 Gas 12,070 274 (NG) 69 166 

Millbury, MA Nov 11–Oct 12 Electricity 10,693 72 (P) ~12, 40-lb bags 

pellets 47 132 

Milton, MA Aug 12–Jul 13 Gas 4,956 361 (NG) 53 94

Quincy, MA Aug 12–Jul 13 Gas 12,046 350 (NG) 76 174

Arlington, MA (2 units) Aug 12–Jul 13 Gas 13,162 688 (NG) 114 222 

Newton, MA Aug 12–Jul 13 Gas 6,974 466 (NG) 70 128

Jamaica Plain-A, MA

(3 units) Aug 11–Jul 12 Gas 6,153 800 (NG) 101 154 

Northampton-A, MA Aug 12–Jul 13 Electricity 7,229 25 82 

Lancaster-A, MA Aug 12–Jul 13 Electricity 8,602 249 (NG) 54.26 124.12 

Brookline, MA Aug 12–Jul 13 Gas 3,321 449 (NG) 56 85 

Westford, MA Aug 12–Jul 13 Gas 10,514 904 (NG) 126.33 214.55 

Gloucester, MA Aug 12–Jul 13 Electricity 15,030 51 171 

Medford, MA (2 units) Aug 12–Jul 13 Gas 14,296 576 (NG) 106 223 

Northampton-B, MA Aug 12–Jul 13 Gas 3,388 472 (NG) 59 88 

Haverhill, MA (2 units) Aug 12–Jul 13 Electricity 11,484 39 131 

Rutland, MA Aug 12–Jul 13 Propane 4,394 468 (P) 58 93
24 

House Location Time Period

Primary 

Heating 

Fuel

Electricity 

(kWh)

Natural Gas 

(therm) or 

Propane (gal)

Other Energy 

Source

Total Site 

Energy 

(MMBtu)

Total 

Source

Energy 

(MMBtu)

Methuen, MA Aug 12–Jul 13 Electricity 12,198 42 139 

Wakefield, RI Sep 12–Aug 13 Propane 6,531 356 (P) 55 107 

Groton, MA Aug 12–Jul 13 Gas 7,763 806 (NG) 107 173

Cohasset, MA Oct 12–Sep 13 Propane 6,494 634 (P) 80 133 

Sudbury, MA Oct 12–Sep 13 Gas 5,017 289 (NG) 46 87 

Northampton-C, MA Sep 12–Aug 13 Gas 4,463 306 (NG) 46 83 

Warwick, MA Nov 12–Aug 13 Electricity 2,725 9 31 

Melrose, MA Dec 12–Sep 13 Electricity 7,289 25 83

Lowell, MA Jan 13–Sep 13 Gas 2,776 220 (NG) 31 55

Waltham, MA Jan 13–Jul 13 Gas 2,590 199 (NG) 29 50 

Jamaica Plain-B, MA Aug 12–Jul 13 Gas 11,153 1,666 (NG) 205 302 

Concord, MA Dec 12–Jun 13 Gas 7,040 1,331 (NG) ~1⁄4 cord wood 162 224 
25 

4.4.1 Energy Use Data Normalization and Disaggregation

Total energy use for a given house is a function of weather conditions during the time period, the 

size of the house, the number of households, the number of residents, and the life style of the 

residents. To compare and analyze the energy use among different houses across different time 

periods, it is necessary to use performance metrics that normalize for at least some of these 

variables. 

Weather conditions vary between different post-retrofit periods. In order to compare post-retrofit 

performance for different time periods, and to compare post-retrofit performance to static 

benchmarks, the energy use data for each project were normalized to “typical” weather conditions 

using a simple linear regression method. Typical Meteorological Year 3 (TMY3) data files were 

selected to represent “typical” weather conditions. TMY3 data files contain weather data meant to 

represent typical conditions at a particular geographic location over a long period of time (Wilcox 

and Marion 2008). 

In most cases, the normalization involved a linear regression of the relationship between monthly 

heating fuel usage and the corresponding monthly heating degree days (HDDs) with a base of 

65°F for the same period. Monthly electrical energy use was evaluated for a relationship to 

cooling degree days (CDDs, also with a base of 65°F) during cooling months. For projects that 

use electricity for heating and cooling (e.g., heat pump system), the linear regression compared 

electrical energy use to HDDs during heating months and to CDDs during cooling months. The 

linear regression factors (slope and intercept) were then applied to monthly HDDs and CDDs 

derived from TMY3 data for the same weather station that provided the HDD and CDD data for 

the post-retrofit period for the project. 

For energy use that is not associated with heating or cooling, the year-to-date usage was combined 

with the normalized heating (or heating and cooling) energy usage to yield a normalized postretrofit annual energy usage. 

For projects that have less than a full year of post-retrofit data, the linear regression factors were 

used to generate heating (or heating and cooling) energy use for a year based on monthly TMY 

weather data. This regression-derived heating and cooling energy was then combined with a year 

of actually non-heating and cooling energy use. In some cases, the year of non-heating and 

cooling energy use included data from months prior to (but not during) the retrofit project. This is 

taken as a reasonable and conservative approximation, given that the non-heating and cooling 

energy use is typically only marginally impacted, and tends to be reduced by the retrofit. 

The normalization resulted in very minor (typically < 5%) adjustments to the total energy use data 

for each project. With the exception of some cases involving electric fuel used for heating and 

cooling, the correlation (R2

) between measured energy use and weather data tended to be 

reasonably good (> 0.9). The weather-normalized data should be viewed as a rough 

approximation, due to the low resolution of the energy use data (approximately monthly), the 

varying correlation accuracy with HDDs (and as applicable, CDDs), and the simple method used.5 

 

5 A previous study conducted by BSC (Osser et al. 2012) found that elaborate methods of weather normalizing 

energy use data provided marginal, if any useful refinement relative to more simple methods.
26 

Heating and cooling energy use were disaggregated from non-heating and cooling energy use 

either by using the linear regression intercept or by identifying minimum monthly heating and/or 

cooling energy use outside of heating and cooling seasons, respectively. It should be noted that 

some portion of domestic hot water (DHW) heating energy use may be captured in the heating 

energy use where the same fuel is used for both DHW and space heating. This is because the inlet 

water temperature to the water heating appliance tends to decrease, thus increasing DHW energy 

use for a given load, as monthly HDDs increase.

Table 9 below presents the normalized post-retrofit site and source energy use as well as the 

normalized post-retrofit heating and cooling site and source energy use for each project.
27 

Table 9. Summary of DER Community Pre- and Post-Retrofit Energy Use, Normalized Post-Retrofit Energy Use, and 

Normalized Heating and Cooling Post-Retrofit Energy Use

House Location 

Pre-Retrofit 

Energy Use

(MMBtu)

Post-Retrofit 

Energy Use

(MMBtu)

(# Months For 

Less Than Full 

Year of PostRetrofit Data)

TMY3 WeatherNormalized PostRetrofit Energy Use

(MMBtu)

TMY3 WeatherNormalized Post-Retrofit 

Heating and Cooling 

Energy Use

(MMBtu)

Site Source Site Source Site Source Site Source

Belchertown, MA 195 211 40 55 44 60 27 28

Belmont, MA (2 units) 451 530 69 166 70 168 34 51

Millbury, MA 125 187 47 132 47 133 19 61

Milton, MA 114 183 53 94 54 95 27 34

Quincy, MA 119 220 76 174 78 176 39 59

Arlington, MA (2 units) 316 402 114 222 112 221 61 83 

Newton, MA 148 215 70 128 73 131 43 55

Jamaica Plain-A, MA

(3 units) 201 269 101 154 113 166 56 60 

Northampton-A, MA 132 173 25 82 27 90 13 43

Lancaster-A, MA 112 158 54 124 54 123 5 18

Brookline, MA 89 118 56 85 58 87 36 38

Westford, MA 209 296 126 215 119 206 68 84

Gloucester, MA 145 189 51 171 49 164 17 56

Medford, MA (2 units) 350 464 106 223 109 226 66 93 

Northampton-B, MA 103 153 59 88 60 90 38 42

Haverhill, MA (2 units) 160 220 39 131 37 124 18 59 

Rutland, MA 113 197 58 93 60 95 19 22

Methuen, MA 109 174 42 139 40 134 15 49

Wakefield, RI 102 179 55 107 55 107 25 28

Groton, MA 152 222 107 173 101 166 64 68

Cohasset, MA 265 367 80 133 83 137 64 78
28 

House Location 

Pre-Retrofit 

Energy Use

(MMBtu)

Post-Retrofit 

Energy Use

(MMBtu)

(# Months For 

Less Than Full 

Year of PostRetrofit Data)

TMY3 WeatherNormalized PostRetrofit Energy Use

(MMBtu)

TMY3 WeatherNormalized Post-Retrofit 

Heating and Cooling 

Energy Use

(MMBtu)

Sudbury, MA 37 125 46 87 44 85 27 35

Northampton-C, MA 71 106 46 83 47 84 28 36

Warwick, MA 48 58 9 31 10 months postretrofit data 11 36 5 17 

Melrose, MA 282 334 25 83 10 months postretrofit data 32 106 14 46 

Lowell, MA 79 135 31 55 9 months postretrofit data 41 70 21 22 

Waltham, MA 85 125 29 50 7 months postretrofit data 46 86 24 25 

Jamaica Plain-B, MA 274 342 205 302 210 307 140 147

Concord, MA 230 353 162 224 7 months postretrofit data 231 340 102 107 
29 

4.5 Characterization of Post-Retrofit Energy Use

4.5.1 Pre- and Post-Retrofit Energy Use Comparison

Figure 2 compares pre-retrofit and post-retrofit site energy use, for the 29 projects for which 

sufficient post-retrofit energy use data were available. The chart indicates where the pre-retrofit 

usage is derived from an energy model as opposed to actual utility bills. Also, for some projects 

for which BSC obtained less than a full year of post-retrofit energy use data, the chart shows postretrofit energy use generated from weather normalization. Figure 3 provides a similar comparison 

in terms of source energy use.

These charts highlight the huge range in pre-retrofit energy use among the group of projects. 

There is a factor of approximately 9 between the minimum and maximum pre-retrofit energy use 

for both site and source energy. There is also variation in the post-retrofit energy use, with a 

similar relative range between the minimum and maximum observations for the comprehensive 

retrofits. However, the absolute magnitude of the spread between the minimum and maximum 

values is much smaller for the post-retrofit energy use. 

It follows from the huge variation in pre-retrofit energy use that the relative reduction of energy 

use achieved would also exhibit significant variation. Figure 4 shows the percent reduction in 

energy use achieved in terms of both site and source energy. For the 27 comprehensive DER 

projects, the site energy use reductions range from a low of 25% and a high of 84%. The median 

site energy use reduction for these projects is 53% and the mean is 55%. In terms of source energy 

use, the reductions range from 10% to 75%. The median source energy use reduction for these 

projects is 44%, the mean is 43%. 
30 

 

Figure 2. Pre- and post-retrofit site energy use for all DER projects
31 

Figure 3. Pre- and post-retrofit source energy use for all DER projects
32 

Figure 4. Energy use reduction (percent reduction) achieved in terms of both site and source energy for all DER projects

Comprehensive DER 

Site Energy Reduction:

Min: 28% 

Max: 84% 

Median: 53% 

Mean: 55%

Comprehensive DER 

Source Energy Reduction:

Min: 10% 

Max: 75% 

Median: 44% 

Mean: 43%
33 

It is tempting to presume that the greater relative reductions among these projects are associated 

with relatively greater pre-retrofit energy use. However, through most of the range of pre-retrofit 

energy use, there is a wide range of energy use reductions. This is demonstrated in Figure 5 and 

Figure 6: the graphs show a “scatter” rather than a relationship. 

Figure 5. Site energy use percent reduction relative to pre-retrofit site energy use 

Figure 6. Source energy use percent reduction relative to pre-retrofit source energy use 
34 

The percentage reduction achievable is dependent on the pre-retrofit state of the house. For 

example, the Brookline retrofit (labeled in Figure 5 and Figure 6) was the final stage of a twostage DER project; the roof and basement components had been completed several years earlier. 

Thus, the 28% source energy use reduction does not capture the effect of the prior stage(s) of 

the DER. 

One might expect that larger homes would exhibit greater relative reductions from a package of 

measures aimed at reducing heating and cooling energy use; however, this is not seen in the data 

(Figure 7 and Figure 8). 

Figure 7. Site energy use percent reduction relative to pre-retrofit conditioned floor area 

Figure 8. Source energy use percent reduction relative to pre-retrofit conditioned floor area 
35 

Neither do the data appear to show a significant relationship between relative energy use 

reduction and either pre-retrofit air leakage (Figure 9 and Figure 10) or age of the home 

(Figure 11 and Figure 12).

Figure 9. Site energy use percent reduction relative to pre-retrofit air leakage measurement 

Figure 10. Source energy use percent reduction relative to pre-retrofit air leakage measurement 
36 

Figure 11. Site energy use percent reduction relative to approximate year of construction 

Figure 12. Source energy use percent reduction relative to approximate year of construction 

From these data there does not appear to emerge a single pre-retrofit factor that can serve as a 

significant predicter of relative energy use reduction for the retrofit package. 

4.5.2 Post-Retrofit Energy Use per Household

Several of the houses in this community are multifamily, therefore an important performance

metric to consider for benchmarking the results is the total energy use per household. This metric 

is computed by dividing the total building energy use by the number of households in the 

building. Figure 13 shows weather-normalized post-retrofit site energy use in MMBtu per 
37 

household for 12 months. Figure 14 shows similar post-retrofit usage in terms of source energy. 

The northeast regional household averages for site and source energy use, derived from data 

available from the Energy Information Administration (EIA), are shown in the figures for 

comparison. 

The U.S. Department of Energy maintains regional energy performance metrics per household 

that are based on information contained in the EIA Residential Energy Consumption Survey 

(RECS). The most recent information available is from 2009 (DOE/EIA 2009). Unless indicated 

otherwise, the regional average energy use presented in this analysis corresponds to this survey 

year. For the Northeast region, the EIA average site energy consumption per household is 107.6 

MMBtu/year. The EIA performance information does not include average source energy 

consumption per household. To convert EIA site energy consumption to source energy use, the 

average site energy use per household was distributed among fuel types according to the 

distribution of the total fuel consumption for the northeast households in the RECS. The 

ENERGY STAR source-to-site ratios (EPA 2011; Table 6) were applied based on this distribution 

yielding an EIA Northeast regional average household source energy use of 174 MMBtu/year. 

Therefore, a 30% reduction in energy use relative to average household source energy use is 122 

MMBtu/year and post-retrofit source energy use of 87 MMBtu/year represents a 50% reduction 

relative to the regional average household. 

According to the latest survey of U.S. housing (U.S. Census Bureau 2013) the average size home 

in the region is 1,900 ft2

. Among the retrofit projects included in this analysis, the median 

conditioned floor area is 2,720 ft2 and the average is 2,956 ft2. This difference in conditioned floor 

area does not necessarily indicate a larger home per se, because almost all of the retrofit houses 

resulted in a conditioned basement and, therefore, include conditioned basement floor area in the 

total conditioned floor area of the home. For a simple volume two-story house with a basement, 

bringing the basement into conditioned space (typically a basement is excluded from conditioned 

space) would increase the conditioned floor area by roughly 50%. Therefore, the sample is 

understood to be reasonably representative of typical housing in the region and the regional 

average is taken to be an appropriate benchmark for per-household energy use. 

In terms of site energy (Figure 13), the median post-retrofit per-household energy use for the 

comprehensive retrofits is 49.2 MMBtu/year while the mean is 52.8 MMBtu/year. Twenty-three

of the comprehensive DER projects, representing 85% of the sample achieved a post-retrofit site 

energy use that is 30% less than the regional average. Fifteen of the projects use less than 50% of 

regional average per household site energy use. 

In terms of source energy (Figure 14), the median post-retrofit per-household energy use is 95.3 

MMBtu/year while the mean is 107.2 MMBtu/year. Eighteen of the comprehensive DER projects, 

representing 67% of the sample, achieved a post-retrofit site energy use that is 30% less than the 

regional average. Nine of the projects use less than 50% of regional average per household site 

energy use.

The Quincy and Westford retrofits, which are the two highest “per household” source energy 

users, are both single-family homes and are the largest in terms of conditioned square feet of the 

single-family homes in this community. This highlights one shortcoming of the “per household” 
38 

performance metric—while it compensates for duplication of appliance and other miscellaneous 

use, it does not take into account the physical size of the home. 

The Gloucester DER is one that involved a conversion to all electrical energy use, including water 

heating. The post-retrofit, per-household source energy usage of this DER is among the highest of 

the group while it is in the middle of the range for site energy use. 
39 

Figure 13. Post-retrofit site MMBtu/year per household

EIA Regional Average Site Use per Household, 107.6 MMBtu/year

50% of EIA Regional Average Site Use per Household

Post-Retrofit Site Energy per Household:

Median: 49.2 MMBtu

Mean: 52.8 MMBtu

Less than 70% of Regional Average: 23 projects

Less than 50% of Regional Average: 14 projects
40 

Figure 14. Post-retrofit source MMBtu/year per household

EIA Regional Average Source Use per Household, 174 MMBtu/year

50% of EIA Regional Average Source Use per Household

Source Energy per Household:

Median: 95.3 MMBtu

Mean: 107.0 MMBtu

Less than 70% of Regional Average: 18 projects 

Less than 50% of Regional Average: 9 projects
41 

4.5.3 Post-Retrofit Energy Use Intensity

A common performance metric used for comparing energy consumption between buildings of 

various sizes is energy use intensity (EUI). This is the energy used per square foot of conditioned 

floor area, often expressed in terms of kBtu per square foot per year (kBtu/ft2

∙yr). Performance

targets of the 2030 Challenge and the Passive House program are expressed in terms of EUI. 

Since the EUI can refer to either source or site energy use, any EUI comparisons using must be 

source-to-source or site-to-site. Also, the calculation of “square footage of floor area” may vary. 

In this report, the conditioned space is determined by the interior dimensions of each floor and 

includes an insulated basement, but does not include insulated, unvented but unfinished attic 

space or crawlspaces.

In 2002, Architecture 2030 established the 2030 Challenge with the ultimate goal of reducing 

fossil fuel, greenhouse-gas emitting energy consumption to zero by 2030, with intermediate goals 

provided along the way. These goals are stated in terms of fossil fuel-generated site energy. 

Therefore, this energy consumption includes all electricity use from the grid as well as natural gas 

and propane use on site. Intermediate reduction goals are stated relative to the building type 

regional average as determined by the 2001 RECS. The 2030 Challenge goal for 2012 is a 60% 

reduction of the average site energy for the particular building type in the region; the goal for 

2015 is a 70% reduction. 

Figure 15 shows the weather-normalized site energy use in site kBtu/ft2

∙yr for the retrofits. The 

figure also indicates the Northeast regional average EUI for 2-4 family and single-family houses 

from the 2001 RECS. The chart also shows the 2030 Challenge’s 2012 and 2015 goals for 

Northeast multifamily (two- to four-unit multifamily houses) and single-family homes. 

All of the comprehensive retrofits perform well below the respective 2001 RECS regional average 

EUI for multifamily and single-family homes. Even without subtracting the portion of energy 

used that is generated on site, three of the single-family retrofits (Warwick, Northampton, 

Melrose) as well as the Haverhill and Belmont two-family DERs meet the Northeast region 2015 

goal of the 2030 Challenge. Six of the single-family DER projects meet the Northeast region 2012 

goal. 

The mean site EUI for the entire group of comprehensive DER projects is less than half of the 

Northeast regional average determined by the 2001 RECS. 

Figure 16 shows weather-normalized post-retrofit source EUI for each of the retrofits in the 

community. Source (or “primary energy”) EUI is one of the metrics used in the Passive House 

program, a program that is universally acknowledged to represent a very rigorous standard for 

new construction building performance. In addition to indicating the regional average (based on 

the most current RECS survey date, 2009) source EUI for single-family and multifamily homes, 

the chart also indicates the nominal source EUI target for the Passive House program. Note that 

there is not a direct correspondence of the source EUI nominal target (38.1 kBtu/ft2

∙yr) to the 

threshold indicated here, as the Passive House program uses different methodology to define 

conditioned floor area than the Residential Energy Services Network (RESNET 2009).
42 

Figure 15. Post-retrofit site EUI (kBtu/ft2

∙yr) 

Architecture2030 Regional Average for Single-Family homes (from 2001 RECS))

2012 Target

2015 Target

Architecture 2030 Regional Average 

for 2–4 Family homes (from 2001 

RECS) 

2012 Target

2015 Target

Architecture 2030 Targets (kBtu/ft2∙yr)

Target 2–4 Family Single-Family

Regional Average

from 2001 RECS

57.8 45.7

2012 Target 23.1 18.3

2015 Target 17.3 13.7
43 

Figure 16. Post-retrofit source EUI (kBtu/ft2

∙yr)

Single-Family Regional Average (2009 RECS)

Approximate Passive House Target

2–4 Family

Regional Average (2009 RECS)

Source EUI Reference Benchmarks (kBtu/ft2∙yr)

Regional Average – Multifamily 78.8

Regional Average – Single-Family 67.5

Passive House (Approximate) 38.1

Single-Family Sample Average: 44.5 kBtu/ft2

∙yr 

Multifamily Sample Average: 51.7 kBtu/ft2∙yr
44 

Nine of the single-family projects and one of the multifamily projects achieved the nominal 

Passive House source EUI threshold. Passive House would count floor area differently including 

only the “net” usable floor area. Thus calculated EUI under Passive House methodology would be 

slightly higher. Still, it appears that at least half of the single-family comprehensive DER projects 

perform at a level close to this very rigorous performance standard. On average, the group of 

single-family DER projects achieved a source EUI of 44.5 kBtu/ft2∙yr while the group of 

multifamily DER projects achieved an average source EUI of 51.7 kBtu/ft2∙yr. 

It is also apparent in Figure 16 that some of the single-family DER projects exceed the regional 

average source EUI and that some of the multifamily DERs in this group performed rather close 

to the regional average for source EUI. This may reflect the selection of low-performance options 

in the DER package, or implementation issues that detract from performance. For example, the 

Medford and Arlington projects excluded the basement from the thermal enclosure of the 

building. The analysis presented in Section 4.2 below, the strategy of excluding the basement 

from the thermal enclosure, results in less effective air leakage control. The Millbury and 

Westford projects are known to have performance problems associated with poorly functioning 

mechanical equipment (Gates and Neuhauser 2013). 

The EUI measure has a bias that favors larger homes (Ueno 2010a). In general, one could think of 

the energy used in a home as representing two kinds of energy use: one is related to supporting 

residential function within the space and is not related to the size of the building (refrigeration, 

cooking, clothes washing). The other kind of energy use—heating for example—is related to 

factors that are tied to the size of the home. In a smaller home, the energy end uses related to 

people using the space (e.g., refrigeration, cooking, washing dishes) are allocated over a smaller 

conditioned floor area, when calculating EUI. 

As shown in Figure 17, there appears to be poor correlation between house size and EUI (R2 

= 

0.17). While there may not be a discernible correlation, it is notable that the two single-family 

comprehensive DER homes with the highest source EUI also have the smallest post-retrofit 

conditioned floor area (Figure 18).

Figure 17. Source EUI relative to post-retrofit conditioned floor area for comprehensive DERs
45 

Figure 18. Post-retrofit source EUI and post-retrofit conditioned floor area 
46 

4.6 Impact of Retrofit Package Variations

In the following sections, the post-retrofit energy use is analyzed for the 27 comprehensive DER 

projects, examining trends associated with the aspects of the National Grid DER package. Given 

that the enclosure and mechanical system measures most directly affect heating and cooling 

energy use, the heating and cooling energy use disaggregated from total post-retrofit energy use is 

presented in this section. 

4.6.1 Heating Fuel Source

Eight of the DER projects switched from primarily fossil fuel heating to electricity-fueled heating 

as part of the retrofit. This configuration of fuels appears to have been pursued as a means to 

reduce the externalities of energy use (e.g., carbon footprint) and also to control energy costs by 

avoiding the significant monthly fees associated with natural gas. 

In high performance retrofit, the configuration of fuel or energy sources is not expected to have a 

significant impact on source energy use. A high efficiency heat pump system is expected to have 

comparable performance to a high efficiency fossil fuel heating system, when performance is 

measured in terms of source energy needed to satisfy the heating load. For a heat pump heating 

system, an overall coefficient of performance of 2.8 represents roughly the same source energy 

impact as a 90 AFUE boiler.6

 Table 10 and Figure 19 show the source EUI for the multifamily 

and single-family DER projects grouped by configuration of heating and water heating fuels. It 

shows that DER homes using a heat pump heating system exhibit the highest and among the 

lowest source EUI for the group. 

Table 10. Heating Fuel and Source EUI

Heating and Cooling EUI

(kBtu/ft2)

Total EUI

(kBtu/ft2)

Heating Fuel No. 

Obs. Range Median Mean Range Median Mean

Single-Family

Electric Heating 7 8.6–32.8 17.1 20.2 17.8–88 67.8 57.5

Dual Fuel Heating 3 11.5–25.1 13.0 16.5 27.8–59.6 38.5 42.0

Fossil Fuel Heating 12 7.9–21.1 14.4 14.5 27.5–52 37.8 37.6

All Single-Family 22 7.9–32.8 15.0 16.6 17.8–88 38.9 44.5

Multifamily

Electric Heating 1 23.1 48.9

Dual Fuel Heating 1 28.9 70.7

Fossil Fuel Heating 3 10.6–22.9 15.5 16.3 35.3–60.9 42.8 46.3

All Multifamily 5 10.6–28.9 22.9 20.2 35.3–70.7 48.9 51.7

 

6 This is a simple mathematical determination based on the relative efficiency of heating systems and the source-site 

ratio of the heating fuel used. For example, with a source-site ratio of 3.34 for electricity and 1.047 for gas, a heat 

pump system with a system efficiency or coefficient of performance of 2.86 will have nearly the same source energy 

impact as a gas furnace heating system with a system efficiency of 0.9 for a given heating load. This simple 

comparison is an approximation as a heat pump heating system will have an efficiency that varies with outdoor 

temperature and that tends to be lower with colder temperatures (i.e., when there are a greater number of heating 

load hours).
47 

The comparatively large range in the heating and cooling source energy use for the single-family

retrofits using electric heating may reflect that the effective system efficiency of these systems is 

highly variable between projects. 

Use of a heat pump for heating or for both heating and DHW does not appear to result in 

noticeably higher source energy use. The three smallest single-family DER projects are among the 

DER projects with heat pump heating and higher source EUI. It has already been discussed how 

EUI has a bias against smaller homes. The multifamily building that used a heat pump for part of 

its heating energy use is also one that excluded the basement from the thermal enclosure. 

Two of the single-family projects, Millbury and Gloucester, exhibit among the four highest source 

EUI measures and have ducted mini-split heat pump systems. BSC previously conducted a postretrofit investigation of one of these projects, which concluded that the heat pump system was 

functioning poorly (Gates and Neuhauser 2013). The performance of ducted (as opposed to 

ductless) mini-split systems might be a topic for further research. 

4.6.2 Included Versus Excluded Basement

One of the enclosure variants among the retrofits was the treatment of the basement. Through the 

project plan review process, BSC strongly advised projects against excluding the basement from 

the thermal enclosure, due to moisture and air quality risk. Some projects persisted with DER 

plans that excluded the basement from the thermal enclosure. In the sample of DER projects 

included in the energy use analysis, there are only two projects that excluded the basement from 

the thermal enclosure. Both of these retrofit projects involve multifamily (two-family) homes.

Figure 20 shows the heating and cooling source EUI for the projects and highlights the two 

projects that excluded the basement from the enclosure. The chart does show that the heating and 

cooling source EUI use for the DER projects that excluded the basement is considerably higher 

than for the other multifamily DERs in the peer group. However, the limited sample size and vast 

number of variables that affect post-retrofit energy use preclude suggesting a directly causal 

relationship. The air leakage analysis section below considers the impact of basement treatment 

on overall air leakage performance.
48 

 

Figure 19. Post-retrofit source EUI grouped by heat and DHW fuel source with post-retrofit conditioned floor area 
49 

 

Figure 20. Post-retrofit heating and cooling source EUI by basement treatment
50 

4.6.3 Unvented Versus Vented Attic

Another variant among the retrofit projects was treatment of the attic. The different approaches 

used were as follows: 

• Vented attic with insulation at the attic floor

• Unvented attic with insulation under the roof deck 

• Unvented attic with exterior insulation over (as well as under) the roof deck. 

Vented attics and unvented attics with all insulation below the roof deck tend to have some heat 

loss at the wall/roof intersection due to the thermal bridging through the framing, and the limited 

insulation that can be installed above the wall top plate. 

Figure 21 shows the post-retrofit heating and cooling source EUI for multifamily and singlefamily comprehensive DER projects grouped by attic and roof treatment. One of these projects 

includes both an unvented attic and a smaller vented attic; it is included in the unvented attic 

group but designated with a different bar in the chart. The mean EUIs for the vented attic DERs 

are appreciably higher than the mean EUIs for the unvented attic DERs. It is not clear that this 

difference is at all associated with the different attic/roof strategy. 

The vented attic strategies applied in all of the vented attic single-family DER projects involved 

adding a completely new (including newly framed) roof and attic. Therefore, these vented attics 

are not representative of typical retrofit vented attic approaches. 

When comparing the two unvented attic approaches, the group of single-family unvented attic 

DERs that applied insulation to the exterior and the underside of the roof deck had only a slightly 

lower mean heating and cooling energy use intensity than the group that employed insulation to 

the underside of the sheathing only. 

A review of the post-retrofit performance for the first 13 DERs that completed projects through 

the pilot found that exterior insulation plus interior insulation appeared to have a slight edge 

(Gates and Neuhauser 2013). In that earlier analysis, the group of DER projects that implemented 

insulation to the exterior of the roof sheathing was the same set of projects that employed the socalled “chainsaw” retrofit technique at the roof-to-wall transition. In this set of DER projects, one 

project (Haverhill) was insulated to the exterior of the roof sheathing, but did not implement a 

chainsaw retrofit. Two other projects with insulation to the exterior of the roof sheathing (Lowell 

and Concord) implemented elements of the chainsaw technique.
51 

 

Figure 21. Post-retrofit heating and cooling source EUI grouped by attic and roof treatment

 
52 

4.6.4 Airtightness Versus Post-Retrofit Energy Use 

Air leakage is a major source of heat loss for homes in a cold climate. Figure 22 and Figure 23 

show post-retrofit heating and cooling source EUI and heating and cooling source energy use per 

household (respectively), relative to the measured airtightness at the completion of the project for 

comprehensive DER projects. 

Figure 22. Post-retrofit heating and cooling EUIs relative to post-retrofit ACH50

Figure 23. Post-retrofit heating and cooling energy use per household 

relative to post-retrofit ACH50

There is not a strong correlation between heating and cooling EUIs or per household and 

airtightness. There does appear to be a general trend of decreasing energy use with lower ACH50 

(as one might expect). 
53 

Most of the projects with a post-retrofit measured ACH50 of 1.5 or less are in the lower energy 

use range, but there is also a noticeable grouping of projects in this airtightness range that exhibit 

post-retrofit energy use that is distinctly above the trendline for the group. 

4.7 Conclusions of Energy Use Analysis

Research Question: What measured savings does the population of DER projects demonstrate?

For the 27 comprehensive DER projects for which sufficient post-retrofit energy use data were

available, the mean reduction in total site energy use achieved is 58% with the site energy use 

reductions for individual projects ranging from 29% to 89%. On a source energy basis, the sample 

exhibits a mean reduction of 41% with a range of 10% to 74%. The authors maintain, however, 

that energy use reduction is not an appropriate metric for comprehensive retrofit. Because preretrofit conditions are highly variable, the relative reduction found in one sample of buildings is 

not necessarily applicable to another sample of buildings or to any one building. The post-retrofit 

performance achieved is a more reliable indicator of the potential benefit from the comprehensive 

DER package.

Research Question: What level of post-retrofit energy performance does the population of DER 

projects demonstrate?

The DER projects were compared to a variety of benchmarks (regional averages, etc.). This 

analysis used weather-normalized post-retrofit energy use for the 27 comprehensive DER projects 

for which sufficient post-retrofit energy use data were available: 

• In terms of household site energy use, all but one project achieved performance that is 

below the EIA Northeast regional average; 14 of the comprehensive DER projects 

achieved performance that is below half of the regional average. The group of projects 

exhibits a mean per household site energy use of 52.8 MMBtu/year, which is slightly less 

than 50% of the regional household average.

• All but two of the comprehensive DER projects achieved household source energy use 

below the EIA Northeast regional household average; nine of the DER projects achieved 

performance that is less than 50% of the regional household average. The mean for the 

group is 107 MMBtu/year, or approximately 38% below the regional household average. 

• In terms of site EUI, all of the comprehensive DER projects perform below the regional 

average with the mean for both the multifamily and single-family DER projects being 

below 50% of the respective Northeast region average. Two of the multifamily projects 

and three of the single-family projects meet the 2015 site EUI goal for the Architecture

2030 Challenge without taking any credit for on-site electricity generation. 

• All but four of the of the single-family DER projects achieved source EUI that is below 

the Northeast regional multifamily and single-family average. Both the single-family and 

multifamily projects achieved a mean source EUI that is 34% lower than the respective 

regional average. One of the multifamily projects and nine of the single-family projects 

achieved a source EUI that is below the nominal primary energy use target in the Passive 

House program for new construction (albeit with different floor area calculations).
54 

Based on this community, this DER package is expected to result in yearly source energy use on 

the order of 110 MMBtu/year or approximately 40% below the Northeast regional average. 

Larger and medium-sized homes that successfully implement these retrofits can be expected to 

achieve source EUI that is comparable to Passive House new construction. 

Whether the National Grid pilot met the aspiration of demonstrating a 50% reduction in energy 

use relative to typical homes in the region depends upon whether the energy use is measured in 

terms of site energy or source energy. By both per-household and EUI metrics the sample of 

DER projects has a mean post-retrofit energy use that is more than 50% below the regional 

average on a site energy basis. On a source energy basis, the post-retrofit performance is less 

than 50% below the regional average. 

Research Question: Do energy performance data show discernible differences that may be 

attributable to variations in the approach to the overall DER package?

No significant trends emerges from analysis of the post-retrofit energy use data. The following 

observations relative to heating and cooling source EUI may suggest topics for further study: 

• DER projects that implemented a heat pump (electric) based heating system exhibited a 

wide range of performance relative to other DER projects. This may indicate significant 

variation in effective heat pump system efficiency. 

• Projects in this sample that exclude the basement from the thermal enclosure exhibit 

higher heating and cooling EUIs than other DER projects in their peer group. With the 

limited number of observations for this variation among the sample, it is not possible to 

assert a direct causal relationship. The data from this study suggest a topic worth 

examining with a more targeted study. 

• Among different approaches to attic and roof retrofit, the DER projects that implemented 

an unvented attic approach appear to have lower heating and cooling energy use on 

average.

• The data show only a vague trend of lower energy use with greater airtightness. The data 

also indicate significant variation in energy use associated with similar levels of 

airtightness. Controlling for some of the other variables in the package implementation, 

such as heating fuel, might reveal a stronger relationship between airtightness and heating 

and cooling energy use.
55 

5 Airtightness Results and Analysis

One requirement for the participants in the National Grid DER pilot program was to provide a 

plan for airtightness, with a target of achieving 0.10 CFM/ft2

 of the building enclosure surface 

area (all six sides) at 50 Pascal air pressure differential (i.e., 0.10 CFM50/ft2 enclosure). Toward 

meeting this goal, participants were asked to identify the air control system for the house and a 

means for ensuring that it was continuous. 

The air control system is a system of materials designed and constructed to control airflow 

between conditioned space and unconditioned space. It is the primary boundary that separates 

indoor (conditioned) and outdoor (unconditioned) air (see Lstiburek 2005 for a primer on the 

subject). The air control system can be located anywhere in the building enclosure: at the exterior 

surface, the interior surface, or anywhere in between. However, it must be continuous over the 

entire enclosure, air impermeable, durable, and able to withstand forces acting on the building, 

both during and after construction. 

The primary purpose of the air control system is to prevent energy loss through direct air 

exchange between the interior and exterior. Since this air exchange also includes air-transported 

moisture, it is also part of the vapor control system. 

Post-retrofit air leakage testing results were obtained for each of the projects participating in the 

pilot therefore the DER project sample in this section includes all 42 DER projects participating in 

the pilot. Table 12 and Table 13 provide airtightness testing results for the full and partial DERs, 

respectively. Results are given for pre-retrofit tests (available in all but three cases), and postretrofit tests. The results are also normalized in terms of air changes per hour at a 50 Pascal air 

pressure differential (ACH50), based on the volume of the house post-retrofit. The materials used 

to create the air barrier at the roof/attic, above-grade wall, and basement ceiling (where 

applicable) were called out per project; the key is shown in Table 11. The final column in Table 

12 and Table 13 shows whether the “chainsaw” retrofit was used at the roof-wall junction 

(Yes/No/Partial).

Table 11. Air Barrier Material/Air Control Layer Key for Data Tables Below

Abbreviation Air Barrier Material/Air Control Layer

CB Taped/sealed ceiling board

DW Drain wrap (corrugated house wrap)

FA Fully adhered membrane

HW House wrap

SPF Spray polyurethane foam insulation

TI Taped rigid insulation

TP Taped panel

TPly Taped plywood

n/a Not applicable
56 

Table 12. DER Community Test Results and Air Control System Properties–Full DERs

House Location 

PreRetrofit 

CFM50

PostRetrofit 

CFM50

Pre-Retrofit 

ACH50

PostRetrofit 

ACH50

Roof/Attic Air 

Control Material 

(See Key Above) 

Above-Grade 

Wall Air Control 

Material 

(See Key Above)

Basement Ceiling 

Air Control 

Material 

(See Key Above)

Chainsaw? 

Yes/No/

Partial 

Belchertown, MA 9,097 468 57.7 1.88 SPF SPF n/a N

Belmont, MA 5,700 590 9.3 0.74 FA HW+TI n/a Y

Millbury, MA 2,860 402 10.4 1.42 FA HW n/a Y

Milton, MA 1,695 584 4.5 1.43 SPF HW n/a N

Quincy, MA 5,050 762 18.5 1.26 HW HW n/a Y

Arlington, MA 8,730 3,586 30.0 7.26 SPF HW old/TP new TI N

Newton, MA 3,199 1,299 10.2 3.56 HW HW n/a Y

Jamaica Plain-A, MA 7,729 1,802 10.9 2.54 SPF sloped/CB flat HW + TI n/a N

Northampton-A, MA 6,155 473 

Pre-retrofit 

volume not 

available

0.82 FA TP n/a Y 

Lancaster-A, MA 4,254 293 36.1 1.43 SPF HW n/a N

Brookline, MA 1,640 655 3.8 1.50 SPF HW + TI n/a N

Westford, MA 2,592 930 4.8 1.22 SPF TPly old/SPF new n/a N

Gloucester, MA 2,258 235 6.6 0.60 FA HW n/a Y

Medford, MA 5,296 1,922 9.9 3.46 SPF sloped/CB flat HW TI N

Northampton-B, MA 1,315 556 4.1 1.12 Poly sheet TPly n/a N

Haverhill, MA 6,970 1,085 18.0 2.54 SPF HW n/a N

Dorchester, MA 13,779 5,084 19.9 7.10 SPF sloped/CB flat HW TI N

Rutland, MA 1,658 493 6.6 1.26 FA HW+TI n/a Y

Methuen, MA 2,452 504 11.6 1.54 CB Nail base insul. n/a N

Wakefield, RI 4,665 222 14.8 0.70 FA FA n/a Y

Groton, MA 2,644 830 4.8 1.51 SPF HW + TI n/a Y

Williamstown, MA 556 2.30 TI HW n/a N

North Kingstown, RI 2,800 1,358 5.6 2.25 SPF SPF n/a N

Cohasset, MA 4,455 1,664 7.4 2.10 TPly HW n/a Y

Sudbury, MA 2,095 224 

Pre-retrofit 

volume not 

available

0.51 FA HW n/a Y 

Worcester, MA 9,779 464 19.5 0.88 FA HW + TI n/a Y

Northampton-C, MA 2,800 453 Pre-retrofit 0.90 FA old/TP new TI old/TP new n/a Y
57 

House Location 

PreRetrofit 

CFM50

PostRetrofit 

CFM50

Pre-Retrofit 

ACH50

PostRetrofit 

ACH50

Roof/Attic Air 

Control Material 

(See Key Above) 

Above-Grade 

Wall Air Control 

Material 

(See Key Above)

Basement Ceiling 

Air Control 

Material 

(See Key Above)

Chainsaw? 

Yes/No/

Partial 

volume not 

available

Warwick, MA 1,689 60 5.9 0.21 FA HW n/a Y

Lexington, MA 4,658 536 18.8 1.26 TP TI n/a Y

Melrose, MA 2,798 434 10.3 1.43 FA DW n/a Y

Providence-A, RI 1,429 1.94 FA HW SPF Y

Roslindale, MA 2.700 1,213 6.4 2.48 FA DW n/a P

Lowell, MA 3.547 340 13.2 0.94 HW old/TP new HW n/a P

Waltham, MA 3,005 677 17.6 2.53 FA HW + TI n/a Y

Northampton-D, MA 7,635 476 11.3 0.70 TP HW n/a Y

Lancaster-B, MA 5,709 1,886 

Pre-retrofit 

volume not 

available

3.00 FA DW SPF Y 

Providence-B, RI 1,134 2.02 FA HW n/a Y

Table 13. DER Community Test Results and Air Control System Properties–Partial DERs

House Location 

PreRetrofit 

CFM50

PostRetrofit 

CFM50

PreRetrofit 

ACH50

PostRetrofit 

ACH50

Roof/Attic Air 

Control Material

(See Key Above) 

Above-Grade 

Wall Air 

Control 

Material

(See Key Above) 

Basement 

Ceiling Air 

Control 

Material

(See Key Above) 

Chainsaw? 

Yes/No/

Partial 

Jamaica Plain-B, 

MA 8,000 4,539 9.9 5.29 SPF n/a n/a N 

Florence, MA 4,094 1,902 6.5 3.07 CB n/a n/a N

Concord, MA 3,376 1,907 5.9 3.33 FA n/a n/a N

Watertown, MA 4,988 2,440 6.3+ 3.04 HW n/a n/a Y
58 

5.1 Airtightness Test Results

Blower door tests were performed on the homes prior to the beginning of the DER construction 

and again after the DER construction was complete. Pre-DER and post-DER total CFM50 blower 

door test results are shown in Figure 24. No pre-DER results are shown for three projects 

(Williamstown, Providence RI-A and Providence RI-B), because demolition work had begun 

prior to engagement with the National Grid program and thus testing could not provide 

meaningful results. 

The percent of total CFM50 reduction between the pre-DER and post-DER is shown in Figure 25. 

For all of the full DER projects, the reduction in total CFM50 was greater than 50%. For the 

partial DER projects, all of which included treatment of the roof or attic but not the exterior walls, 

the reduction in total CFM50 was from 40% to 55%. 

The CFM50 measure represents an absolute measure of air leakage not normalized to building 

geometry. This metric is useful, for example, to gauge the impact on air leakage of a particular 

renovation project regardless of how or whether the renovation might have changed the area of 

the enclosure or the volume of space enclosed. 

The National Grid pilot program established an enclosure airtightness target in terms of CFM50 

per enclosure area. This metric provides a standard of airtightness performance for the enclosure 

components retrofit as well as those components for which the retrofit is incentivized. 

Air changes per hour induced by a 50 Pascal pressure difference (ACH50) is a more common 

measure for building airtightness. It is used in the ENERGY STAR and Passive House programs, 

for example. Because the measured air leakage rate at an induced pressure difference is expressed 

relative to the volume of enclosed space, the ACH50 measure can be thought of as normalized to 

building size. 

When the airtightness results are normalized to ACH50 (air changes per hour at a differential of 

50 Pascals), more than half of the full-DER projects achieve an airtightness of 1.5 ACH50 or 

better (see Figure 26).

All but two projects among the full-DER projects have airtightness results meeting that required 

for ENERGY STAR v3 homes. These two projects, Dorchester and Arlington, which are obvious 

outliers in terms of airtightness for the DER community, established the lower air control layer at 

the basement ceiling rather than including the basement within the air control enclosure. It has 

been observed in the past that this often results in significant air leakage through the basement 

ceiling (Ueno and Lstiburek 2012). 

In order to assess how variations in the DER package might impact airtightness performance, it is 

important to first check whether other significant factors such as size, age, and pre-retrofit 

condition of the building impact post-retrofit performance. As can be seen by the scatter graphs in 

Figure 27, there is no apparent relationship between the post-DER airtightness results achieved 

and the size, the age/vintage, or the pre-DER airtightness conditions of the house. 
59 

Figure 24. Pre-DER and post-DER total CFM50 results

0

2000

4000

6000

8000

10000

12000

14000

Belchertown

Belmont

Millbury

Milton

Quincy

Arlington

Newton

Jamaica Plain-A

Northampton-A

Lancaster-A

Brookline

Westford

Gloucester

Medford

Northampton-B

Haverhill

Dorchester

Rutland

Methuen

Wakefield, RI

Groton

Williamstown

North Kingstown, RI

Cohasset

Sudbury

Worcester

Northampton-C

Warwick

Lexington

Melrose

Providence, RI-A

Roslindale

Lowell

Waltham

Northampton-D

Lancaster-B

Providence, RI-B

Jamaica Plain-B

Florence

Concord

Watertown

Jamaica Plain-C

Pre CFM50 Post CFM50

Full DER Partial DER
60 

Figure 25. Percent reduction from pre-DER to post-DER total CFM50

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Belchertown

Belmont

Millbury

Milton

Quincy

Arlington

Newton

Jamaica Plain-A

Northampton-A

Lancaster-A

Brookline

Westford

Gloucester

Medford

Northampton-B

Haverhill

Dorchester

Rutland

Methuen

Wakefield, RI

Groton

North Kingstown, RI

Cohasset

Sudbury

Worcester

Northampton-C

Warwick

Lexington

Melrose

Roslindale

Lowell

Waltham

Northampton-D

Lancaster-B

Jamaica Plain-B

Florence

Concord

Watertown

Jamaica Plain-C

Full DER Partial DER

Percent CFM 50 Reduction 
61 

Figure 26. Post-DER ACH50 results

Post-DER Conditioned Square Feet Year House Built Pre-retrofit total CFM50

Figure 27. Post-DER ACH50 versus size of house, year house was built, and pre-DER total CFM50

0

1

2

3

4

5

6

7

8

Warwick

Sudbury

Gloucester

Northampton-D

Wakefield, RI

Belmont

Northampton-A

Worcester

Northampton-C

Lowell

Northampton-B

Westford

Quincy

Lexington

Rutland

Millbury

Lancaster-A

Melrose

Milton

Brookline

Groton

Methuen

Belchertown

Providence, RI-A

Providence, RI-B

Cohasset

North Kingstown, RI

Williamstown

Roslindale

Waltham

Jamaica Plain-A

Haverhill

Lancaster-B

Medford

Newton

Dorchester

Arlington

Watertown

Florence

Concord

Jamaica Plain-B

Jamaica Plain-C

Full DER Partial DER

ACH 50

1.5 ACH 50

ENERGY STAR v3 Air tightness: 4.0 ACH 50

0

1

2

3

4

5

6

7

8

0 1000 2000 3000 4000 5000 6000

Post-DER cond s.f.

ACH 50

0

1

2

3

4

5

6

7

8

1750 1800 1850 1900 1950 2000

Year house was built

ACH 50

0

1

2

3

4

5

6

7

8

0 5000 10000 15000

Pre-retrofit total CFM 50

ACH 50
62 

5.2 Analysis of Airtightness and DER Package Variations

In the following subsections, the airtightness results for the full DERs are analyzed with respect to 

several variations within the implementation of the DER measures that may be expected to have 

an impact on the airtightness results. These variables include inclusion/exclusion of basement in 

air control enclosure, vented/unvented attic, and air control materials. 

5.2.1 Inclusion/Exclusion of Basement in Air Control Enclosure

The DER measures did not specify whether the basement was to be included in the thermal and 

air control enclosures. In general, it is better to include the basement in the thermal and air control 

enclosures because (1) mechanical equipment and ductwork is typically located there (resulting in 

regain of duct/pipe thermal losses); (2) this approach reduces the dampness commonly associated 

with a basement if executed correctly; and (3) it is very difficult to establish an effective air 

separation between the basement and the rest of the house due to the many penetrations and 

framing connections in the basement ceiling (Ueno and Lstiburek 2012). 

As shown in Figure 28, five of the projects chose to exclude the basement from the thermal and 

air control enclosure. The results from this group support the previous argument that air 

separation is difficult to achieve at the basement ceiling. During the blower door testing of the 

Arlington project, it was noted that roughly half of the total air leakage from the building was 

occurring through the basement ceiling (Neuhauser 2011). 

As indicated in Figure 28, two of the projects for which the basement was excluded used SPF 

insulation in the basement ceiling framing for the air control layer, while the other three used 

taped rigid insulation panels for the air control layer. The two retrofits with SPF insulation in the 

basement ceiling have better airtightness results than those that used taped rigid insulation, but 

these are still significantly leakier than the mean for the group of projects that included the 

basements. 

Garages and unconditioned crawlspaces with living space above can create similar difficulties in 

establishing an air separation as basement ceilings, though generally there are fewer (if any) 

penetrations to be accommodated. The projects that included the basement but also have these 

other conditions are shown as subgroup in Figure 28. 

Since exclusion of the basement appears to be a significant factor in air leakage results, these 

projects are distinguished in the analysis charts in the remainder of this section.
63 

Figure 28. Post-DER ACH50 results grouped by treatment of basement

 

0

1

2

3

4

5

6

7

8

Providence, RI-A

Providence, RI-B

Medford

Dorchester

Arlington

Wakefield, RI

Westford

Melrose

Roslindale

Lancaster-B

Warwick

Sudbury

Gloucester

Northampton-D

Belmont

Northampton-A

Worcester

Northampton-C

Lowell

Northampton-B

Quincy

Lexington

Rutland

Millbury

Lancaster-A

Milton

Brookline

Groton

Methuen

Belchertown

Cohasset

North Kingstown, RI

Williamstown

Waltham

Jamaica Plain-A

Haverhill

Newton

Location of Basement 

AirControl

at Foundation walls

Mean: 1.52

Median: 1.42

at Bsmt Ceiling

Mean: 2.47 

Median: 2.02 

w/o Arlington & 

Dorchester ACH 50

Crawl space 

or Garage 

Ceiling

Mean: 1.77;

Median: 1.43

No Crawl space or 

Garage Ceiling

Mean: 1.47

Median: 1.42

SPF insulation in basement, garage, or crawlspace ceiling
64 

5.2.2 Vented/Unvented Attic

The DER measures did not specify whether the upper thermal and air control layers were to be at 

the attic floor (vented attic) or at the roof plane (unvented attic). Seven of the DER projects 

established the thermal and air control layers at the attic floor (or top floor ceiling). The air control 

layer was at the roof plane for all of the other full-DER projects.

For a retrofit, establishing an air barrier between the attic and the conditioned space below can be 

hindered by the ceiling and roof framing, knee walls, or partition walls in the floor below. 

However, the more difficult air control problem is to create a continuous connection between the 

air control layer at the attic floor and the air control layer of the exterior wall. This is particularly 

difficult when the air control layer for the wall is on the exterior of the wall, as is the case for all 

except one of the DER projects: the air barrier must be transitioned across the thickness of the 

built-out wall.

A similar continuity problem may exist with an unvented attic when the air control layer is to the 

interior side of the roof, but is to the exterior side of the wall. If there is discontinuity of air 

control across this transition, there will be air leakage at the intersection of the roof and the 

exterior wall. On the other hand, if the air control layers for the roof and for the wall are both to 

the exterior, the connection between the two is straightforward if the rafter tails and rake

overhangs are cut off before the air control layers are applied. The roof air control layer can then 

lap over (and be sealed to) the wall air control layer, thus eliminating the air leakage at the 

intersection. This technique is commonly referred to as the “chainsaw” approach (Orr and 

Dumont 1987; Holladay 2009).

Figure 29 groups the DERs by vented and unvented attics, and then the unvented attics by 

chainsaw, partial chainsaw, or non-chainsaw air control. The partial chainsaw retrofits are those 

that used the chainsaw approach for only part of the house. While the Dorchester and Arlington 

projects are shown in their appropriate groups, these projects are not included in computing the 

means and medians for the groups because of their outlier status. 

The results for the vented attic group show that very good airtightness results can be obtained 

when a new attic or roof is being built as part of the overall project. While this may not be typical 

for a retrofit, it can occur when the retrofit project is combined with the addition of space (as was 

the case for Northampton-B, Lancaster-A and Methuen). With careful sequencing of the 

construction, the air control continuity at the intersection of the wall and the attic can be 

established before the new rafters or trusses are put in place. The Williamstown project also 

included a new space over one portion of the existing house, but parts of the existing attic were 

retained. 

The mean and medians for the full chainsaw group were better than those of the partial chainsaw 

and the non-chainsaw group, as well as those of the vented attic group. In addition, the chainsaw 

group includes the nine best airtightness results of all of the DERs. 
65 

Figure 29. Post-DER ACH50 results grouped by treatment of attic/roof treatment

0

1

2

3

4

5

6

7

8

Northampton-B

Lancaster-A

Methuen

Williamstown

Jamaica Plain-A

Medford

Dorchester

Westford

Milton

Brookline

Belchertown

North Kingstown, RI

Haverhill

Arlington

Lowell

Roslindale

Warwick

Sudbury

Gloucester

Northampton-D

Wakefield, RI

Belmont

Northampton-A

Worcester

Northampton-C

Quincy

Lexington

Rutland

Millbury

Melrose

Groton

Providence, RI-A

Providence, RI-B

Cohasset

Waltham

Lancaster-B

Newton

Vented Attic

Meanw/o Dorchester: 2.06

Median w/o Dorchester: 1.92

Meanw/o Arlington: 1.50

Median w/o Arlington: 1.42

Non-chainsaw Air

Control Layer;

Mean w/o 

Arlington: 1.80

Median w/o 

Arlington: 1.69

Chainsaw AirControl Layer

Mean: 1.40

Median: 1.26

New

attic & 

roof

Unvented Attic

ACH 50

Air control at basement ceiling

Partial chainsaw Air Control Layer: Mean & Median: 1.71
66 

5.2.3 Air Control Materials

The airtightness results are primarily a function of the following factors and sub-factors:

• Roof/attic and above-grade wall air control layers

o Material

o Location 

o Installation 

• Effectiveness of the connection between the air control layers of different components 

o Roof/attic to exterior wall

o Exterior wall to window/door 

o Exterior wall to foundation wall/basement ceiling. 

In the previous sections, the location and some aspects of the installation and connections have 

been compared. In this section, the comparisons are based primarily on air control materials for 

the roof/attic and for the above-grade walls. 

The materials and approaches used for above grade wall air control in these projects included: 

• Taped and sealed house wrap or drain wrap (corrugated house wrap) applied over the 

existing sheathing (majority of projects)

• Taped oriented strand board (OSB) panels

• Taped plywood panels 

• Taped rigid insulation 

• Fully adhered membrane over the existing sheathing (one project) 

• SPF insulation on the interior (one project). 

All of the projects with an exterior wall air control layer also applied insulation to the exterior of 

the walls: most projects used taped foil-faced polyisocyanurate, while other choices included 

semi-rigid mineral wool and nail base insulation panels. Several of the projects that used taped 

and sealed house wrap also incorporated the exterior insulating sheathing into the wall air control 

layer by sealing all of the layers together at the assembly perimeter and at openings. 

For the vented attic air control layer, most projects used a layer of SPF insulation, taped ceiling 

board, or a combination of SPF insulation and taped ceiling board. One project used a continuous 

polyethylene sheet between the attic and the living space below. 

The unvented attic approaches can be divided into interior- and exterior-side air barriers. The 

projects that used an interior air control layer under the roof deck used SPF insulation. The 

projects that used exterior air control used taped and sealed house wrap, taped OSB panels, or 

fully adhered roof membrane. In most (but not all) cases with an exterior air control roof layer, 

exterior insulation in the form of taped foil-faced polyisocyanurate was applied over the air 

control layer. The exceptions were Lexington, Providence RI-A and Providence RI-B: they all 
67 

used an exterior air control layer on the roof, but all insulation is on the interior side of the roof 

deck.

In Figure 30, the projects are grouped first according to the type of roof/attic air control material 

and then according to the type of wall air control material. The term panel includes OSB panels, 

plywood panels, rigid insulation panels, or ceiling board panels; house wrap includes drain wrap. 

As outliers, the Dorchester and Arlington projects are not included in the computation of any of 

the means.

Among the four groupings based on roof air control material, the group that used fully adhered 

membrane for the roof air control is the largest group, has the second best airtightness result, and 

contains many of the best individual airtightness results. The best group airtightness result is for 

the “Others” group. This group is not well characterized by the roof air control material: it

includes two projects that use different air control materials on different sections of the roof and 

the vented attic project that uses a sheet of polyethylene on the attic floor. 

When the wall air control material subgrouping is also included, there is a marginally consistent 

pattern within each of the roof groups of taped panels for walls having the best results, then taped 

house wrap plus insulating sheathing, and then taped house wrap. 

Many of these projects used SPF insulation in either the wall or the roof/attic component, though 

this was not always relied upon as the air control material. SPF insulation is air impermeable, 

creates a seal with the framing elements when applied per manufacturer’s instructions, and is 

relatively easy to apply as a continuous layer even where there is limited access. Therefore, its use 

could be expected to improve the robustness of the air control system. 

The normalized airtightness results grouped by SPF and non-SPF (in roof and walls) are shown in 

Figure 31. As a group, use of SPF insulation for both the walls and the roof has better ACH50 

results than when the SPF insulation is used only for one or the other (or for only parts of the 

walls or roof). But the group with the best ACH50 result is the group that does not use SPF 

insulation at all in the walls or roof. These projects used cellulose or batt insulation for the cavity 

insulation, and did not rely on cavity insulation for air control. 
68 

Figure 30. Post-DER ACH50 results grouped roof and wall air control material

0

1

2

3

4

5

6

7

8

Northampton-C

Northampton-B

Lowell

Lexington

Methuen

Northampton-D

Williamstown

Westford

Arlington

Belchertown

North Kingstown, RI

Brookline

Groton

Jamaica Plain-A

Lancaster-A

Milton

Haverhill

Medford

Dorchester

Quincy

Roslindale

Newton

Northampton-A

Belmont

Worcester

Rutland

Waltham

Warwick

Sudbury

Gloucester

Millbury

Melrose

Providence, RI-A

Providence, RI-B

Cohasset

Lancaster-B

Wakefield, RI

Roof AC: 

Fully adhered membrane;

Mean: 1.34

Roof/Attic AC: 

SPF or SPF/Ceiling board;

Mean excluding Arlington & 

Dorchester: 1.98

Roof AC: 

Taped housewrap;

Mean: 2.43 Wall AC: Taped

housewrap; Mean 2.43

Wall AC: Taped panels; Mean 1.01

Wall AC: Taped panels; Mean 1.40

Wall AC: Tapedhousewrap; Mean 2.21

Wall AC: Taped panels; 0.82

Wall AC:Tapedhousewrap; Mean 1.47

Wall AC: Fully adhered membrane; 0.70

ACH 50

Fully adhered roof membrane that is not for air control

Roof/Attic AC: 

Taped panels;

Mean: 1.45

Roof/Attic AC:

Other or combination 

of materials; 

Mean: 0.99

Wall AC: Taped housewrap; 0.94

Wall AC: Taped housewrap; Mean: 1.50

Wall AC: combination of materials: 1.22

Wall AC: SPF; Mean 2.06

Taped housewrap + insul panels; Mean: 1.35

Wall AC: Taped housewrap+ insul panels: Mean: 1.85

Air control at basement ceiling
69 

Figure 31. Post-DER ACH50 results grouped use of SPF insulation in walls and roof

0

1

2

3

4

5

6

7

8

Sudbury

Worcester

Quincy

Lancaster-A

Belchertown

Providence, RI-A

Providence, RI-B

North Kingstown, RI

Wakefield, RI

Westford

Lexington

Millbury

Milton

Brookline

Groton

Cohasset

Jamaica Plain-A

Haverhill

Lancaster-B

Medford

Newton

Dorchester

Arlington

Warwick

Gloucester

Northampton-D

Belmont

Northampton-A

Northampton-C

Lowell

Northampton-B

Rutland

Melrose

Methuen

Williamstown

Roslindale

Waltham

No SPF insulation in 

Walls or Roof/Attic

Mean: 1.26

Median: 1.03

SPF insulation 

in Walls and 

in Roof/Attic;

Mean: 1.52

Median: 1.65

SPF insulation in all or part of Walls or 

Roof/Attic but not all of both; 

Mean w/o Dorchester and Arlington: 2.02:

Median w/o Dorchester and Arlington: 1.51

SPF insul is all or part of air control layer for roof/attic SPF insul is all or part of air control layer for roof & walls Air control at bsmt ceiling
70 

In the previous sections where air control material was not included in the information, the group 

of projects that used a chainsaw air control approach had the best overall result. Figure 32

combines the use of fully adhered membrane on the roof as the air control layer (or simply as an 

underlayment) with the chainsaw technique. The projects that used taped panels for the wall air 

control layer are also highlighted. Only DERs with unvented attics are shown in Figure 32. 

In the group with the fully adhered roof membrane, the mean of projects that used the chainsaw 

technique is 5% less than the mean of the full group that used a fully adhered roof membrane; the 

median of the chainsaw subgroup is about 25% less. The nine DERs with the best individual 

airtightness results in the DER community are in this subgroup. For the group without a fully 

adhered roof membrane, the mean is slightly greater for the chainsaw subgroup, and the median is 

slightly less. It is likely that both the fully adhered material and the chainsaw technique play a role 

in achieving the better airtightness results.
71 

Figure 32. Post-DER ACH50 results grouped by non-adhered/fully adhered roof underlayment 

0

1

2

3

4

5

6

7

8

Lowell

Quincy

Lexington

Milton

Groton

Belchertown

North Kingstown, 

...

Roslindale

Newton

Arlington

Warwick

Sudbury

Gloucester

Northampton-D

Wakefield, RI

Belmont

Northampton-A

Worcester

Northampton-C

Westford

Rutland

Millbury

Melrose

Brookline

Providence, RI-A

Providence, RI-B

Cohasset

Waltham

Haverhill

Lancaster-B

Unvented Roof with non-adhered underlayment 

and air control: Mean w/o Arlington: 1.84; 

Median w/o Arlington: 1.51

Unvented Roof with fully adhered underlayment or air control

Mean: 1.35; Median: 1.24

Meanw/ Chainsaw: 

1.90

Median w/ Chainsaw: 

1.38

Mean w/ Chainsaw: 1.28

Median w/ Chainsaw: 0.90

Non-chainsaw air control Chainsaw air control

ACH 50

Air control at basement ceiiling
72 

5.3 Airtightness Trends Observed in the DER Community

The following trends were observed in the National Grid Pilot DER community that consists of 37 

full DERs and five partial DERs. 

Research Question: What level of post-retrofit airtightness performance does the population of 

DER projects demonstrate?

• All full DER projects achieved better than 50% reduction in total CFM50; all partial DER 

projects achieved better than 40% reduction in total CFM50. 

• All but two of the full DER projects achieved a post-retrofit ACH50 below the ENERGY 

STAR threshold for climate zones 5–7. For over half of the full DER projects, the postDER ACH50 results are 1.5 ACH50 or better. The mean post-DER ACH50 for the group 

of full DER projects is 1.9 ACH50. 

Research Question: Do post-retrofit airtightness data show discernible differences that may be 

attributable to variations in the approach to the overall DER package?

• The group of DER projects that included the basement in the air control enclosure had a 

better overall airtightness result than the group that excluded the basement (i.e., 

insulation and air control at basement ceiling).

• The group of DER projects with unvented attics had a better overall airtightness result 

than the group with vented attic. 

• The group of DER projects with unvented attics that used the chainsaw approach for the 

wall to roof air control layer connection had a better overall airtightness result than the 

group with unvented attic that did not use the chainsaw approach. 

• The group of DER projects with unvented attic that used a fully adhered roof membrane 

had a better overall airtightness result than the group with unvented attic that did not use 

a fully adhered roof membrane. The airtightness result for the subgroup that used a fully 

adhered roof membrane and used the chainsaw approach was slightly better and included 

the nine best individual airtightness results for the DER community.
73 

6 Construction Cost Analysis

Prior to participating in the National Grid DER pilot, prospective participants completed a series 

of application forms that provided information about the planned DER project. Among the 

information required was projected cost information for the specific DER measures. These 

measures correspond to the enclosure components, air sealing (if provided as a separate cost 

item), and heating, cooling, and ventilation costs. The contractor for the prospective team 

provided the measure cost information that is included in the application. The cost information in 

the application typically reflects the contractual cost for implementation of these measures. 

Therefore the cost reported is the cost to the homeowner, as opposed to the contractor’s cost to 

implement the measure. The costs in the contract may not reflect the final cost to the homeowner 

where changes were pursued after the start of the project. Also, contractors are likely to exhibit 

significant variations in how total project costs are apportioned to various measures. 

As part of the cost information provided in the application, a distinction was made between 

“allowable” and “non-allowable” costs. The “allowable” costs are items that are specifically 

implemented for reducing energy use (e.g., additional insulation or replacing an old inefficient 

boiler with a 95%-rated AFUE boiler), while the “non-allowable” costs are for items that are not 

related to reducing energy use (e.g., replacing roofing or siding). The Deep Energy Retrofit 

Multifamily and Single-family Pilot Guidelines (National Grid 2011) provide the following 

guidance relative to distinguishing allowable from non-allowable costs:

Allowable project costs eligible for incentives are limited to net incremental costs, 

of implementing the DER measures. For example; for super insulation on wall 

exterior, the customers’ costs of the insulation material, its installation, special 

attachments and trim modifications required to accommodate the super insulation 

would be eligible for incentives, whereas costs for the new siding (or cladding 

such as stucco) and its installation would not. 

This breakdown was intended primarily to determine the costs eligible for incentive payments, but 

is also useful to break down costs into energy-related and non-energy (e.g., aesthetic) related 

costs. It should be noted that reported project costs relate to the retrofit project only. If, for 

example, the larger project between the contractor and the homeowner included such items as new 

kitchens cabinets and countertops, costs for such items are not included in the project cost 

considered in this analysis. 

6.1 Summary of Energy-Related Construction Costs

Table 14 shows the total project costs and the total energy-related project costs for each of the 

DER projects as reported in the applications. In addition, the energy-related portion of the project 

costs are divided into enclosure measure costs and HVAC measure costs. 

Table 15 provides shows project costs for the partial DERs and indicates what measures were 

implemented.
74 

Table 14. Summary of National Grid DER Project Costs as Derived From Program Application Forms—Full DERs

House Location Total DER 

Project Cost

Total EnergyRelated DER 

Measures Cost

Projected EnergyRelated DER Enclosure 

Measures Cost

Projected Energy-Related DER 

HVAC Measures Cost 

(With Some DHW)

Belchertown, MA $64,629 $51,642 $35,045 $16,597 (no cooling in cost)

Belmont, MA (2 units)a $212,357 $174,762 $142,094 $32,668

Millbury, MA $82,719 $71569 $49,894 $21,675

Milton, MA $77,651 $66,236 $51,236 $15,000

Quincy, MA $127,197 $108,515 $68,915 $39,600

Arlington, MA (2 units) $125,240 $95,163 $69,537 $25,626 (cooling coil; no 

condenser)

Newton, MA $148,039 $97,039 $65,539 $31,500

Jamaica Plain-A, MA (3 units) $214,313 $180,678 $165,528 $15,150 (ventilation only in cost)

Northampton-A, MA $237,791 $119,701 $85,061 $34,640

Lancaster-A, MAb $76,510 $57,446 $47,408 $10,038

Westford, MA $117,712 $107,464 $94,080 $13,384 (no heating in cost)

Gloucester, MA $142,317 $89,165 $70,665 $18,500

Medford, MA (2 units) $114,153 $88,767 $66,167 $22,600

Northampton-B, MA $79,350 $56,350 $46,350 $10,000 (heating only in cost)

Haverhill, MA (2 units) $131,200 $104,200 $83,200 $21,000

Dorchester, MA (3 units) $158,701 $113,951 $81,650 $32,301

Rutland, MA $99,905 $79,490 $56,820 $22,670 (no cooling in cost)

Methuen, MA $113,340 $73,340 $56,340 $17,000

Wakefield, RI $78,953 $77,953 $70,953 $7,000 (ventilation only in cost)

Groton, MAc $167,980 $167,980 $128,030 $38,950

Williamstown, MA** $36,181 $31,564 $21,564 $10,000 (no cooling in cost)

North Kingston, RI (2 units) $130,412 $95,860 $61,860 $34,000

Cohasset, MA $132,564 $70,814 $59,921 $10,893

Sudbury, MA $157,506 $105,611 $88,861 $16,750

Worcester, MA (3 units) $143,207 $108,307 $84,307 $24,000

Northampton-C, MA $228,902 $112,971 $108,771 $4,200 (ventilation only in cost)

Warwick, MAb $100,210 $88,762 $80,070 $8,692

Lexington, MA $79,151 $66,161 $49,861 $16,300 (no cooling in cost)

Melrose, MA $165,284 $124,184 $116,544 $17,000

Providence-A, RI (3 units) $251,806 $194,352 $148,728 $45,624 (no cooling in cost)

Roslindale, MA $146,235 $145,085 $141,885 $3,200 (ventilation only in cost)
75 

House Location Total DER 

Project Cost

Total EnergyRelated DER 

Measures Cost

Projected EnergyRelated DER Enclosure 

Measures Cost

Projected Energy-Related DER 

HVAC Measures Cost 

(With Some DHW)

Lowell, MA $81,605 $56,555 $53,555 $3,000 (ventilation only in cost)

Waltham, MA $74480 $59,729 $47,449 $12,280

Northampton-D, MA (2 units) $255,581 $111,387 $84,722 $15,000

Lancaster-B, MA (2 units) $177,450 $103,210 $88,210 $15,000

Providence-B, RI (3 units) $210,988 $139,465 $99,965 $39,500 (no cooling in cost) a DER measure costs for this project are taken from a post-project analysis produced by the homeowner with input from the contractor. b Volunteer labor was used in this project. c Total project costs for this project did not include non-energy-related items.
76 

Table 15. Summary of National Grid DER Project Costs as Derived from Program Application Forms—Partial DERs

House Location DER Measures

Total 

Project 

Cost

Total EnergyRelated DER 

Measures Cost

Projected EnergyRelated DER Enclosure 

Measures Cost

Projected Energy-Related 

DER HVAC Measures 

Cost

Brookline Walls, windows, 

HVAC $135,774 $73,055 $58,850 $14,205 (no cooling in cost) 

Jamaica Plain-B, MA* Roof, HVAC $52,410 $52,410 $50,010 $2,400 (ventilation only in 

cost)

Florence, MA Attic, basement, 

HVAC $83,446 $82,665 $55,815 $26,850 (no cooling in cost) 

Concord, MA Roof $45,555 $31,201 $31,201 $0

Watertown, MA

(2 units)

Roof, basement, 

HVAC (1 unit) $134,516 $67,128 $51,128 $16,000 

Jamaica Plain-C, MA (3 units) Roof, HVAC $102,154 $49,980 $9,978 $40,002 (heating only in 

cost)

* Total project costs for this project did not include non-energy-related items. 
77 

There is considerable variation between projects in the DER measure costs. While many factors 

will affect variation in project cost, the size of the project will have a very significant impact. 

Therefore, total and energy-related DER measure costs are shown normalized by post-retrofit 

conditioned floor area (Figure 33) and by post-retrofit six-sided enclosure area (Figure 34), for the 

full DER projects. 

When normalized by conditioned floor area, the total energy-related costs for the full DER 

projects range from $16.17/ft2 to $54.04/ft2, with an average of $34.59/ft2 of post-retrofit 

conditioned floor area. 

When normalized to total enclosure area, the energy-related costs for the full DER projects range 

from $7.83/ft2 of enclosure to $26.47/ft2 of enclosure with an average of $16.51/ft2 of enclosure. 

Since most of the DER measures involve the enclosure, the full DER cost metric in terms of 

enclosure area may be more meaningful.
78 

Figure 33. Total project and total energy-related costs normalized by conditioned floor area for full DER projects

$0/sf

$20/sf

$40/sf

$60/sf

$80/sf

$100/sf

$120/sf

Belchertown

Belmont

Millbury

Milton

Quincy

Arlington

Newton

Jamaica Plain-A

Northampton-A

Lancaster-A

Westford

Gloucester

Medford

Northampton-B

Haverhill

Dorchester

Rutland

Methuen

Wakefield, RI

Groton

Williamstown

North Kingstown, RI

Cohasset

Sudbury

Worcester

Northampton-C

Warwick

Lexington

Melrose

Providence, RI-A

Roslindale

Lowell

Waltham

Northampton-D

Lancaster-B

Providence, RI-B

Total reported project cost Total energy related cost

Cost per cond. sf
79 

Figure 34. Total project and total energy-related costs normalized by enclosure area for full DER project

$0/sf

$5/sf

$10/sf

$15/sf

$20/sf

$25/sf

$30/sf

$35/sf

$40/sf

Belchertown

Belmont

Millbury

Milton

Quincy

Arlington

Newton

Jamaica Plain-A

Northampton-A

Lancaster-A

Westford

Gloucester

Medford

Northampton-B

Haverhill

Dorchester

Rutland

Methuen

Wakefield, RI

Groton

Williamstown

North Kingstown, RI

Cohasset

Sudbury

Worcester

Northampton-C

Warwick

Lexington

Melrose

Providence, RI-A

Roslindale

Lowell

Waltham

Northampton-D

Lancaster-B

Providence, RI-B

Total reported project cost Total energy related cost

Cost per enclosure sf
80 

The scope of the DER also impacts the cost. For the full DERs, the scope of work on the 

enclosure is not dramatically different between projects, but with the introduction of partial DERs, 

only the treated part of the enclosure is relevant. Figure 35 shows the total energy-related

enclosure measures cost (excluding the HVAC measure), normalized by the treated enclosure area 

for full and partial DER projects. 

The range of energy-related enclosure costs per treated enclosure area for all DER projects is 

$5.35/ft2 of treated enclosure to $27.65/ft2 of treated enclosure with an average of $13.57/ft2 of 

treated enclosure.

For both full and partial DERs, the scope of the HVAC measure depends primarily on the number 

of separate living units in the building, the condition of the existing mechanical equipment, health 

and combustion safety issues, and the homeowner’s goals. The energy-related HVAC measure 

cost includes those costs in the HVAC measure which directly or indirectly reduce energy use for 

the home. For example, exhaust only ventilation is acceptable for the HVAC measure to meet the 

air quality and health requirements of the DER, but it is not related to energy reduction. So while 

these contribute to the total HVAC measure cost, they are not included in the energy-related part 

of the HVAC measure cost. Figure 36 normalizes the total energy-related HVAC measure costs 

by number of living units, and then groups them according to the functions of the equipment 

installed for the HVAC measure.

For projects that installed HVAC equipment (all of which directly or indirectly reduce energy 

use), the HVAC measure cost ranged from $7,500 to $39,600 per living unit, with an average of 

$16,560. 

For projects that installed energy-reducing heating and ventilation only, or cooling and ventilation 

only, the range was from $10,000 to $38,950 per living unit with an average of $18,195. 

The two projects that provided heating only averaged $11,670 per living unit. Those that provided 

ventilation only (HRV or ERV) ranged from $7,000 to $2,400 per living unit with an average of 

$4,140. 
81 

Figure 35. Total energy-related enclosure costs normalized by treated enclosure area for all DER projects

$0/sf

$5/sf

$10/sf

$15/sf

$20/sf

$25/sf

$30/sf

Belchertown

Belmont

Millbury

Milton

Quincy

Arlington

Newton

Jamaica Plain-A

Northampton-A

Lancaster-A

Westford

Gloucester

Medford

Northampton-B

Haverhill

Dorchester

Rutland

Methuen

Wakefield, RI

Groton

Williamstown

North Kingstown, RI

Cohasset

Sudbury

Worcester

Northampton-C

Warwick

Lexington

Melrose

Providence, RI-A

Roslindale

Lowell

Waltham

Northampton-D

Lancaster-B

Providence, RI-B

Brookline

Jamaica Plain-B

Florence

Concord

Watertown

Jamaica Plain-C

Energy-related enclosure cost

Cost per treated enclosure sf

Full DER Partial DER
82 

Figure 36. Total energy-related HVAC costs normalized by living units in building and grouped by function

$0

$5,000

$10,000

$15,000

$20,000

$25,000

$30,000

$35,000

$40,000

$45,000

Belmont

Millbury

Milton

Quincy

Newton

Northampton-A

Lancaster-A

Gloucester

Medford

Haverhill

Dorchester

Methuen

North Kingstown, RI

Cohasset

Sudbury

Worcester

Warwick

Watertown

Melrose

Waltham

Northampton-D

Lancaster-B

Belchertown

Arlington

Brookline

Rutland

Florence

Groton

Williamstown

Lexington

Providence, RI-A

Providence, RI-B

Westford

Northampton-B

Jamaica Plain-C

Jamaica Plain-A

Jamaica Plain-B

Wakefield, RI

Northampton-C

Roslindale

Lowell

Concord

Project Cost: full HVAC Project Cost: Heating & Ventilation Only Project Cost: Cooling & Ventilation only Project Cost: Heating only Project Cost: Ventilation Only

Cost of HVAC measure per living unit
83 

6.2 Energy-Related Construction Costs per DER Measure

In the following sections, the energy-related construction costs are broken up into the individual 

DER measures as provided in the application. 

6.2.1 Attic/Roof DER Measure

Figure 37 shows the cost per attic/roof sf for all of the full DER projects, and the partial DER 

projects that implemented this measure. The projects are grouped according to the approach taken 

for the implementation.

For those projects that provided attic floor insulation, the costs range from $4.21/ft2

 to $16.00/ft2

with an average of $8.40/ft2. For those projects that provided roof cavity insulation, the range is 

from $6.24/ft2 to $18.39/ft2 with an average of $11.59/ft2. 

The energy-related costs for roof exterior and rafter cavity insulation do not include the cost of 

new roofing. In this group, there are five outlier projects—three with extremely low costs and two

with significantly higher costs than the other projects. Excluding these outliers, the range is from 

$10.05/ft2 to $21.84/ft2 with an average of $14.21/ft2. 

The last group (labeled “Other”) is projects that have vented attics but also sloped ceilings on 

portions of the upper floor, which is a combination of attic floor insulation and rafter cavity 

insulation. The costs for this group range from $6.66/ft2 to $10.25/ft2 with an average of $8.50/ft2. 

6.2.2 Exterior Wall DER Measure 

Figure 38 shows the energy-related costs for implementing the above-grade exterior wall DER 

measure. 

One of the DER projects implemented the exterior wall DER measure by constructing a stud wall 

to the interior of the wall framing and filling the widened wall cavity with insulation. All of the 

other projects added insulation to the exterior of the existing wall. Where there was no existing 

wall cavity insulation, it was installed. If there was existing wall cavity insulation, it was upgraded 

(generally from the exterior) as needed. 

For the projects with exterior insulation, there are three outlier projects–two with extremely low 

costs and one with significantly higher costs. Excluding these outlier projects, the energy-related 

costs for exterior walls range from $4.67 to $19.15 per wall square foot with an average cost of 

$10.51/ft2

. The cost of re-siding is not included in the energy-related cost for those projects with 

exterior insulation, nor is the cost of the additional framing included for the double wall 

implementation. 

These figures are higher than the cost presented by Ueno (2010b) of $4/ft2

. However, that figure 

was from early work before the development of mature contractor pricing. The same contractor 

who provided the original pricing later updated this figure to the $7/ft2

 to 15/ft2 range, depending 

on access, complexity of detailing, and other secondary factors.

The range of unit costs reported for this measure is somewhat surprising given that the scope for 

this measure is similar across the projects.
84 

Figure 37. Total energy-related attic roof costs per attic/roof square foot

$0/sf

$5/sf

$10/sf

$15/sf

$20/sf

$25/sf

$30/sf

$35/sf

Lancaster-A

Northampton-B

Florence

Methuen

Williamstown

Belchertown

Milton

Arlington

Westford

Jamaica Plain-B

North Kingstown, RI

Lexington

Providence, RI-A

Lowell

Providence, RI-B

Belmont

Millbury

Quincy

Newton

Northampton-A

Gloucester

Haverhill

Rutland

Wakefield, RI

Groton

Cohasset

Sudbury

Worcester

Northampton-C

Warwick

Concord

Watertown

Jamaica Plain-C

Melrose

Roslindale

Waltham

Northampton-D

Lancaster-B

Jamaica Plain-A

Medford

Dorchester

Energy-related attic/roof

measure

cost per attic/roof sf

Attic floor 

insulation

Roofrafter cavity 

insulation

Roof exterior and rafter cavity insulation Other

Full DER Partial DER 
85 

Figure 38. Total energy-related exterior wall costs per wall square foot

$0/sf

$5/sf

$10/sf

$15/sf

$20/sf

$25/sf

$30/sf

Belchertown

Belmont

Millbury

Milton

Quincy

Arlington

Newton

Jamaica Plain-A

Northampton-A

Lancaster-A

Brookline

Westford

Gloucester

Medford

Northampton-B

Haverhill

Dorchester

Rutland

Methuen

Wakefield, RI

Groton

Williamstown

North Kingstown, RI

Cohasset

Sudbury

Worcester

Northampton-C

Warwick

Lexington

Melrose

Providence, RI-A

Roslindale

Lowell

Waltham

Northampton-D

Lancaster-B

Providence, RI-B

Exterior and wall cavity insulation

Cavity insulation only

Energy-related wall measure cost per wall sf

Full DER Partial DER
86 

7 Homeowner Satisfaction

A survey was sent to all participants 6 months after the close of the pilot; 12 homeowner 

responses were received. The survey requested information on the homeowner’s objectives in 

deciding to undertake a DER, the benefits of the DER after completion, the challenges of the 

project, any detrimental consequences of the DER, and additional comments not addressed 

elsewhere. A blank survey is included in the Appendix. 

The majority of the respondents noted energy savings (in general or as reduced fossil fuel 

consumption or reduced carbon footprint) and improved comfort as some of their initial reasons 

for considering a DER; four noted additional living space and two noted they wished to be 

examples of how to complete a DER successfully. 

In the post-DER responses, cost was noted in a number of the surveys—from cost overruns to 

equipment costs and estimating. Because of the cost, two projects would reconsider doing the 

below-grade insulation and sub-slab work, which they eventually did complete. 

Complaints on the general contractor and subcontractor were noted in the Milton, Sudbury, 

Lowell, and Northampton-C responses. Scheduling, uncooperative building inspectors, and lead 

time for ordering equipment/windows were other issues noted in several projects.

The Sudbury, Warwick, and Medford homes noted they would not use spray foam again due to 

the environmental concerns of the blowing agents and off-gassing. The Medford house would 

consider alternatives to rigid foam board as well.

A number of projects (the Williamstown, Arlington, Lowell, and Concord homes) would either 

upgrade the HRV equipment or rework the ductwork and placement of the HRV. A few projects 

noted they were impressed with the improved air quality of their homes post-DER.

The Milton project was the only home to note considerable detrimental post-DER consequences, 

which included insect infestation in the closed-cell attic foam, issues of cell phone reception due 

to interference from the foil-faced exterior foam, and additional home maintenance (cleaning the 

HRV filter and cleaning the exterior foam insect barrier). 

Aside from the Milton project, the majority of the responses were very positive with respect to the 

work that was completed under the National Grid program and meeting their expectations for 

comfort and energy reduction. However, there were some issues with the complexity of the 

program (i.e., deciphering the program and how to meet the requirements almost always required 

additional help), how to better coordinate the subcontractors (i.e., including the subs much earlier 

in the process) and how to disseminate the accumulated knowledge from each project going 

forward to improve the National Grid program and to encourage others to participate. 
87 

8 Conclusions

Research Question: What measured savings does the population of DER projects demonstrate?

For the 27 comprehensive DER projects for which sufficient post-retrofit energy use data were 

available, the mean reduction in total site energy use achieved is 58% with the site energy use 

reductions for individual projects ranging from 29% to 89%. On a source energy basis, the sample 

exhibits a mean reduction of 41% with a range of 10% to 74%. The authors maintain, however, 

that energy use reduction is not an appropriate metric for comprehensive retrofit. Because preretrofit conditions are highly variable, the relative reduction found in one sample of buildings is 

not necessarily applicable to another sample of buildings or to any one building. 

Research Question: What level of post-retrofit energy performance does the population of DER 

projects demonstrate?

The DER projects were compared to a variety of benchmarks (regional averages, etc.). This 

analysis used weather-normalized post-retrofit energy use for the 27 comprehensive DER projects 

for which sufficient post-retrofit energy use data were available:

• In terms of household site energy use, all but one project achieved performance that is 

below the EIA Northeast regional average; 14 of the comprehensive DER projects 

achieved performance that is below half of the regional average. The group of projects 

exhibits a mean per household site energy use of 52.8 MMBtu/year, which is slightly less 

than 50% of the regional household average. 

• All but two of the comprehensive DER projects achieved household source energy use 

below the EIA Northeast regional household average; nine of the DER projects achieved 

performance that is below half of the regional household average. The mean for the group 

is 107 MMBtu/year, or approximately 38% below the regional household average. 

• In terms of site EUI, all of the comprehensive DER projects perform below the regional 

average with the mean for both the multifamily and single-family DER projects being 

below 50% of the respective Northeast region average. Two of the multifamily projects 

and three of the single-family projects meet the 2015 site EUI goal for the Architecture 

2030 Challenge without taking any credit for on-site electricity generation.

• All but four of the single-family DER projects achieved source EUI that is below the 

Northeast regional single-family average. Both the single-family and multifamily projects

achieved a mean source EUI that is 34% lower than the respective regional average. One 

of the multifamily projects and nine of the single-family projects achieve a source EUI 

that is below the nominal primary energy use target in the Passive House program for 

new construction (albeit with different floor area calculations). 

Based on this community, this DER package is expected to result in yearly source energy use on 

the order of 110 MMBtu/year or approximately 40% below the Northeast regional average. 

Larger to medium sized homes that successfully implement these retrofits can be expected to 

achieve source EUI that is comparable to Passive House new construction.
88 

Whether the National Grid Pilot met the aspiration of demonstrating a 50% reduction in energy 

use relative to typical homes in the region depends upon whether the energy use is measured in 

terms of site energy or source energy. By both per-household and EUI metrics the sample of 

DER projects has a mean post-retrofit energy use that is more than 50% below the regional 

average on a site energy basis. On a source energy basis, the mean post-retrofit performance is 

between 35% and 40% below the regional average.

Research Question: Do energy performance data show discernible differences that may be 

attributable to variations in the approach to the overall DER package?

No significant trends emerges from analysis of the post-retrofit energy use data. One plausible 

interpretation of this is that the heating and cooling energy use has been reduced to the point 

where relatively minor variations to an otherwise consistent package have little discernible 

impact. The following observations relative to heating and cooling source EUI may suggest topics 

for further study:

• DER projects that implemented a heat pump (electric) based heating system exhibited a 

wide range of performance relative to other DER projects. This may indicate significant 

variation in effective heat pump system efficiency.

• Projects in this sample that exclude the basement from the thermal enclosure exhibit 

higher heating and cooling EUI than other DER projects in their peer group. With the 

limited number of observations for this variation among the sample, it is not possible to 

assert a direct causal relationship. The data from this study suggest a topic worth 

examining with a more targeted study.

• Among different approaches to attic and roof retrofit, the DER projects that implemented 

an unvented attic approach appear to have lower heating and cooling energy use on 

average.

• The data show only a vague trend of lower energy use with greater airtightness. The data 

also indicate significant variation in energy use associated with similar levels of 

airtightness. Controlling for some of the other variables in the package implementation, 

such as heating fuel, might reveal a stronger relationship between airtightness and heating 

and cooling energy use.

BSC conducted analysis of airtightness achieved by projects in the National Grid pilot DER 

community based on pre- and post-retrofit measurements for 37 full DERs and five partial DERs. 

Research Question: What level of post-retrofit airtightness performance does the population of 

DER projects demonstrate?

• All but two of the full DER projects achieved a post-retrofit ACH50 below the ENERGY 

STAR threshold for climate zones 5–7. 

• For over half of the full DER projects, the post-DER ACH50 results are 1.5 ACH50 or 

better. 

• The mean post-DER ACH50 for the group of full DER projects is 1.9 ACH50. 
89 

• All full DER projects achieved better than 50% reduction in total CFM50; all partial DER 

projects achieved better than 40% reduction in total CFM50. 

Research Question: Do post-retrofit airtightness data show discernible differences that may be 

attributable to variations in the approach to the overall DER package?

• The group of DER projects that included the basement in the air control enclosure had a 

better overall airtightness result than the group that excluded the basement (i.e., 

insulation and air control at basement ceiling). 

• The group of DER projects with unvented attics had a better overall airtightness result 

than the group with vented attics. 

• The group of DER projects with unvented attics that used the chainsaw approach for the 

wall to roof air control layer connection had a better overall airtightness result than the 

group with unvented attic that did not use the chainsaw approach. 

• The group of DER projects with unvented attic that used a fully adhered roof membrane 

had a better overall airtightness result than the group with unvented attic that did not use 

a fully adhered roof membrane. The airtightness result for the subgroup that used a fully 

adhered roof membrane and used the chainsaw approach was slightly better and included 

the nine best individual airtightness results for the DER community. 

Research Question: What are the total DER project costs? 

There is no question that high performance retrofit—especially a comprehensive high 

performance retrofit—represents a significant cost. In this DER community, reported project costs 

ranged from slightly more than $36,000 to almost $255,600. The reported energy-related portion 

of the project costs ranged from slightly more than $31,500 to approximately $194,350. Further 

analysis of the reported project costs yields some interesting observations. 

• Relative to post-retrofit conditioned floor area, the reported energy-related costs average 

$34.59/ft2

 for the DER community. This is well below a reasonable cost for attaining a 

similar level of performance in new construction. Even the upper level of the range at 

$54.04/ft2 compares favorably to the cost of high performance new construction. 

Research Question: What are the unit costs of major retrofit measures?

• The cost of HVAC measures varied significantly with the maximum observation of 

$39,600 being more than five times the lower observation of $7,500. The variations in 

HVAC measure costs appear to relate to homeowner preferences and to not appear to be 

correlated with a noticeable difference in performance with the possible exception of one 

project that installed a ground-source heat pump. But with this single observation it is not 

possible to assert a causal relationship.

• The energy-related portion of roof/attic measures show some trends for different 

approaches where the reported cost for a vented attic approach with insulation at the attic 

floor averaged $8.40/ft2

, the unvented attic approach with rather cavity insulation only 

averaged $11.59/ft2, and the unvented attic with insulation both exterior to the roof 

sheathing and between roof framing averaging $14.21/ft2

. 
90 

• Excluding some noted outliers, the reported energy-related cost for the most typical wall 

retrofit approach ranged from $4.67/ft2 to $19.15/ft2 with an average of $10.51/ft2. This 

range is surprising given the relatively uniform scope of work for this measure. The range 

may be indicative of variations in how contractors allocate project costs to various 

measures.

Research Question: What benefits do participating homeowners associate with DER projects 

implemented through this pilot program? 

• Twelve of the homeowner participants in the DER pilot responded directly to a request for 

feedback through a survey distributed by National Grid. The majority of the respondents 

noted energy savings and improved comfort among their initial reasons for considering a 

DER. It is interesting to note that in some cases the survey responses indicated the energy 

reduction goal in general terms and in other cases, energy reduction was expressed in 

terms of reduced fossil fuel consumption (several projects switched to all-electric site 

energy use) and reduced carbon footprint. 

The paucity of survey respondents and difficulties encountered in obtaining useful energy use data 

are noteworthy given that provision of such information was a contractual obligation associated 

with the generous utility program incentives. This portends difficulties in obtaining useful postretrofit data from similar communities of retrofit projects. Direct metering of energy use with 

direct access to the metering data for monitors/research may resolve the issue with energy use 

data. As for the qualitative feedback, direct interviews with participants may prove more useful 

than a survey. 
91 

References

Architecture 2030 (2006). “2030 Challenge Targets: U.S. Regional Averages.” An initiative of 

Architecture 2030. http://architecture2030.org/files/2030_Challenge_Targets_Res_Regional.pdf. 

Accessed December 20, 2012. 

Aspen Publishing. (2013). “Capturing Accuracy for the Residential Remodel Simulation”. pp. 6–

11, Energy Design Update, volume 33, number 10. 

Bianci, M.V.A., editor. (2011). Challenges and Opportunities to Achieve 50% Energy Savings in 

Homes: National Laboratory White Papers. Golden, CO: National Renewable Energy 

Laboratory. Available at http://energy.gov/sites/prod/files/2013/11/f5/ba_tech_roadmap_0.pdf. 

Accessed February 13, 2014. 

DOE/EIA. (2009). Residential Energy Consumption Survey: 2009 RECS Survey Data Fuel 

Consumption and Expenditures: Table CE2-2. Household Fuel Consumption in the Northeast 

Region, Totals and Averages, 2009, British Thermal Units (Btu), Preliminary. 

Donnelly, K.; Mahle, M. (2012). Chamberlain Heights Redevelopment: A Large Scale, Cold 

Climate Study of Affordable Housing Retrofits. Golden, CO: National Renewable Energy 

Laboratory, NREL/SR-5500-53561. 

Eisenberg, L.; Shapiro, C.; Fleischer, W. (2012). Retrofit Audits and Cost Estimates: A Look at 

Quality and Consistency. Golden, CO: National Renewable Energy Laboratory, NREL/SR-5500-

55217. 

EPA. (2011). “ENERGY STAR Performance Ratings Methodology for Incorporating Source 

Energy Use.” www.energystar.gov/ia/business/evaluate_performance/site_source.pdf. Accessed 

November 5, 2013. 

Gates, C.; Neuhauser, K. (2013). Evaluation of Early Performance Results for Massachusetts 

Homes in the National Grid Pilot Deep Energy Retrofit Program. Golden, CO: National 

Renewable Energy Laboratory, NREL/SR-5500-58585. 

Holladay, M. (2009) “Musings of an Energy Nerd: The History of the Chainsaw Retrofit.” Green 

Building Advisor, www.greenbuildingadvisor.com/blogs/dept/musings/history-chainsaw-retrofit, 

August 14, 2009. Accessed November 2013. 

Lstiburek, J. (2005). “Understanding Air Barriers.” ASHRAE Journal 47(7): 24–30, Atlanta, GA: 

American Society of Heating, Refrigeration, and Air-Conditioning Engineers, Inc. 

www.buildingscience.com/documents/digests/bsd-104-understanding-air-barriers. 

McIlvaine, J.; Saunders, S.; Bordelon, E.; Baden, S.; Elam, L.; Martin, E. (2013). The Next Step 

Toward Widespread Residential Deep Energy Retrofits. Golden, CO: National Renewable 

Energy Laboratory, NREL/SR-5500-57978. 
92 

National Grid. (2009). “Deep Energy Retrofit Pilot Description and Guidelines.” A document 

prepared by the Massachusetts energy efficiency Program Administrator for pilot participants 

and state regulators.

National Grid. (2011). “Deep Energy Retrofit Multifamily and Single-family Pilot Guidelines.” 

A document prepared by the Massachusetts energy efficiency Program Administrator for pilot 

participants and state regulators. 

Neuhauser, K. (2011). “BA-1111: National Grid Deep Energy Retrofit Pilot.” Somerville, MA: 

Building Science Corporation, www.buildingscience.com/documents/bareports/ba-1111-

national-grid-der-pilot/view. Accessed August 17, 2012. 

Neuhauser, K. (2012). “BA-1205: Attic or Roof? An Evaluation of Two Advanced 

Weatherization Packages.” Somerville, MA: Building Science Corporation, 

www.buildingscience.com/documents/bareports/ba-1311-evaluation-two-ceda-weatherizationpilot-implementations/view. Accessed October 29, 2012. 

NJIT. (2013). “Re-Side Tight, Ventilate Right: Final Report.” New Jersey Institute of 

Technology. Prepared by The Center for Building Knowledge at NJIT, Newark, NJ for Public 

Service Electric and Gas. 

Orr, H.W.; Dumont, R.S. (1987) “A Major Energy Conservation Retrofit Of A Bungalow.” 

Saskatoon, SK: National Research Council Canada/Institute for Research in Construction, 

Internal Report No. 540. 

Osser, R.; Neuhauser, K.; Ueno, K. (2012). “BA-1107: Final Retrofit Pilot Community 

Evaluation Report.” Somerville, MA: Building Science Corporation. www.buildingscience.com/ 

documents/bareports/ba-1107-final-retrofit-pilot-community-evaluation-report/view. Accessed 

March 4, 2013. 

RESNET. (2009). “Chapter Eight RESNET Standards.” Residential Energy Services Network. 

http://resnet.us/standards/DRAFT_Chapter_8_July_22.pdf. Accessed December 2012. 

Spanier, J.; Scheu, R.; Brand, L.; Yang, J. (2012). Chicagoland Single-Family Housing 

Characterization. Golden, CO: National Renewable Energy Laboratory, NREL/SR-5500-55089. 

Straube, J. (2011). “BA-1005: Building America Special Research Project: High R-Value 

Enclosures for High Performance Residential Buildings in All Climate Zones.” Somerville, MA: 

Building Science Corporation. www.buildingscience.com/documents/bareports/ba-1005-

building-america-high-r-value-high-performance-residential-buildings-all-climate-zones/view. 

Accessed August 5, 2012. 

Ueno, K. and J.F. Straube. (2010). “Building Science Digest 151: Understanding Primary/Source 

and Site Energy.” Somerville, MA: Building Science Corporation. 

www.buildingscience.com/documents/digests/bsd151-understanding-primary-source-siteenergy/. Accessed December 20, 2012. 
93 

Ueno, K. (2010a). “Building Science Digest 152: Building Energy Performance Metrics.” 

Somerville, MA: Building Science Corporation, http://www.buildingscience.com/documents/ 

digests/bsd152-building-energy-performance-metrics/ Accessed December 20, 2012. 

Ueno, K. (2010b). “Residential Exterior Wall Superinsulation Retrofit Details and Analysis”

Performance of the Exterior Envelopes of Whole Buildings XI. Atlanta, GA: American Society of 

Heating, Refrigeration, and Air-Conditioning Engineers, Inc. 

Ueno, K. and J.W. Lstiburek. (2012). “BA-1108: Hybrid Foundation Insulation Retrofits: 

Measure Guideline.” Somerville, MA: Building Science Corporation, 

http://www.buildingscience.com/ documents/bareports/ba-1108-hybrid-foundations-retrofitsmeasure-guideline/view. Accessed August 17, 2012. 

U.S. Census Bureau. (2013). American Housing Survey for the United States: 

2011. http://www.census.gov/programs-surveys/ahs/. Accessed December 23, 2013. 

Wilcox. S.; Marion,W. (2008). Users Manual for TMY3 Data Sets. Golden, CO: National 

Renewable Energy Laboratory, NREL/TP-581-43156. www.nrel.gov/docs/fy08osti/43156.pdf. 

Accessed December 20, 2012. 
94 

Appendix: Homeowner Survey

Deep Energy Retrofit (DER) Homeowner Experience Survey 

Before you started this project, what were your top 5 (or so) objectives when you set out 

to undertake the DER? (examples–Energy savings, additional livable space, improved 

comfort, etc...) If you can, list or number these in order of importance to you (at the 

time).

If energy savings appears on your list, please tell us more. Can you further prioritize 

objectives relative to energy savings? 

Examples– 

Reduce energy costs

“Hedge” against potential energy cost increases in the future 

Reduce environmental impact (e.g. climate change)

Reduce social/geopolitical impact (e.g. national security)

Now that the project is complete, what are the top 5 (or so) benefits that you think your 

project accomplished? If you can, list or number these in order of importance to you.

Examples–energy savings, additional livable space, improved comfort, passive 

survivability (in case of power outage or heating equipment failure), reduced noise from 

outdoors, basement water and moisture management, confidence that pre-existing 

structural and envelope problems have been corrected, confidence that major exterior 

upgrade should not be necessary in the next 30 years, improved indoor air quality, 

improved durability, radon mitigation

What challenges did you encounter in implementing the DER project?
95 

What would you do differently if you were to do this project again?

Are there any detrimental consequences of the DER project? 

We welcome any additional thoughts you would like to share:

Thank you for participating in the National Grid DER Homeowner Experience Survey!
buildingamerica.gov

DOE/GO-102014-4371 ▪ March 2014

Printed with a renewable-source ink on paper containing at 

least 50% wastepaper, including 10% post-consumer waste.